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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 25 of 30

Field Case Study Troubleshooting

Real-world AGL investigation records where the fault wasn't obvious from a single reading — CCR trips tied to weather and intensity steps, isolated single-fixture failures, collateral cable damage, transformer failures after flooding and under load, burned connectors, hidden underground insulation failure, intermittent earth faults, repeat LED failures, PAPI and photometry anomalies, alignment and water ingress findings, stop bar and ALCMS control failures, and a full airfield-wide recurring-failure root cause analysis. Each case follows the full engineering diagnostic record: symptom → observation → measurement → decision → fault location → root cause → verification → corrective action → preventive action.

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01 · Field Case Investigations (20)

01 · Field Case Investigations

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FCS-581 CCR Trip After Rain

Symptom — A CCR serving a runway edge lighting circuit repeatedly tripped on earth-fault protection during and shortly after rainfall events, with the circuit testing normal in dry conditions, prompting a dedicated wet-weather field investigation.

Equipment / System

Primary series circuit cable, joints, and pull boxes along the affected runway edge lighting circuit, and the CCR's earth-fault protection relay.

Possible Causes
HighA degraded joint seal allowing rainwater to bridge a marginal insulation defect only under wet conditions
HighA pull box with a failed lid seal collecting standing water during heavy rain
MedA cable jacket nick from a previous, undocumented repair that only becomes conductive when wet
MedCCR earth-fault relay set at an overly sensitive threshold reacting to a normally acceptable leakage increase
LowA nearby lightning strike coinciding with rain events, causing confusion between two distinct causes
LowRising groundwater at one specific low point along the route
Required Tools
1000V/2500V insulation resistance tester (megger)CCR earth-fault trend log correlated with weather station dataMoisture detection meterTDR / fault locator
Safety Precautions
  • LOTO before all cable/joint work.
  • Treat repeated wet-weather trips as an active hazard rather than a nuisance pattern.
Diagnostic Procedure
  1. ObservationCorrelate the CCR trip log precisely against rainfall timing and intensity from the site weather station over several events.
  2. MeasurementMegger the circuit in segments during a dry period to establish a baseline, then repeat immediately after the next rain event.
  3. MeasurementIdentify the segment showing the largest resistance drop between the dry and wet readings.
  4. DecisionDrop isolated to one segment/joint → excavate and repair that specific point. Drop distributed across many segments → treat as circuit-wide ageing requiring a broader replacement plan.
  5. Fault LocationPinpoint the specific joint or pull box responsible using the wet/dry differential.
  6. Root CauseConfirm the repaired point no longer shows a wet/dry differential over a subsequent rain event.
Test Points
Segment insulation resistance, dry vs. wet
CCR earth-fault trip log vs. weather data
Joint/pull box seal condition at the identified location
Root Cause Verification

Monitor the CCR trip log through at least two subsequent significant rain events after repair and confirm no recurrence.

Corrective Action
  • Reseal or replace the failed joint/pull box seal.
  • Repair the identified cable jacket defect.
Preventive Action
  • Correlate periodic insulation testing with weather timing rather than testing only in dry conditions.
  • Prioritise seal inspection ahead of the wet season on circuits with any trip history.
Related References

SOP: SOP-FCS-01 (Field Case Investigation Procedure), SOP-CBL-04

Standards: IEC 60364, FAA AC 150/5340-30

Diagram: Circuit route drawing with joint/pull box locations

Case Study Cross-Reference: Division 13 — Cable Water Ingress / Failure After Rain (CBL-352, CBL-367); Division 01 — CCR Troubleshooting

Rev 0 — Initial issue
FCS-582 CCR Trip at Maximum Intensity

Symptom — A CCR operated correctly at low and medium intensity steps but tripped on overcurrent/earth-fault protection specifically when commanded to the maximum intensity step, with the circuit passing a standard insulation resistance test at lower voltage.

Equipment / System

Primary series circuit insulation system, evaluated specifically under the higher voltage stress present at maximum CCR output.

Possible Causes
HighA marginal insulation defect in a joint or cable section with a breakdown voltage low enough to pass at lower steps but fail at maximum output
HighA transformer with a degrading winding that only breaks down under the higher voltage stress of full intensity
MedA connector with a small air gap causing corona/arcing only at higher voltage
MedThe CCR itself producing an output waveform anomaly (harmonic distortion) specifically at maximum step, stressing the circuit
LowA design margin issue where the circuit's total transformer count is near the CCR's rated capacity, causing voltage stress at maximum output
LowA nuisance trip from the CCR's own protection calibration at the top of its range
Required Tools
High-potential (hipot) test setCCR output waveform analyser/oscilloscope1000V insulation resistance tester (megger)Transformer test set
Safety Precautions
  • LOTO before hipot testing.
  • Hipot testing uses elevated voltages and must only be performed by qualified personnel with appropriate PPE.
Diagnostic Procedure
  1. ObservationConfirm the trip is repeatable specifically at maximum intensity and not at any lower step, ruling out a simple overcurrent condition.
  2. MeasurementPerform a hipot test on circuit segments at a voltage representative of maximum CCR output to find the marginal defect that standard megger testing missed.
  3. MeasurementTest individual transformers for a winding that only leaks under higher voltage stress.
  4. DecisionHipot test identifies a specific segment/transformer → targeted repair or replacement. No specific point identified → investigate CCR output quality and circuit loading margin.
  5. Fault LocationIsolate to the specific segment, joint, or transformer failing under elevated voltage.
  6. Root CauseConfirm the circuit holds at maximum intensity over a full test cycle after repair.
Test Points
Hipot test result per segment at elevated voltage
Individual transformer winding test under load
CCR output waveform at maximum step
Circuit transformer count vs. CCR rated capacity
Root Cause Verification

Operate the CCR at maximum intensity for an extended period after repair and confirm no trip recurs.

Corrective Action
  • Replace the identified marginal cable/joint section.
  • Replace the failing transformer.
  • Address a CCR output waveform issue with the manufacturer/vendor.
Preventive Action
  • Include a periodic hipot test, not just standard megger, for circuits with any history of intensity-dependent faults.
  • Review circuit loading margin against CCR capacity during any circuit extension.
Related References

SOP: SOP-FCS-02 (Field Case Investigation Procedure)

Standards: IEC 60502, FAA AC 150/5340-30

Diagram: Circuit loading and transformer schedule

Case Study Cross-Reference: Division 01 — CCR Troubleshooting; Division 13 — High Resistance Joint (CBL-355)

Rev 0 — Initial issue
FCS-583 One Light Failure in Healthy Circuit

Symptom — A single fixture went dark while every circuit-level test (CCR current, insulation resistance, continuity) returned normal readings, suggesting the fault was isolated entirely within the fixture or its immediate connection rather than the circuit.

Equipment / System

The individual fixture, its isolation transformer, and the L-823 connector pair at that specific location, evaluated in isolation from the otherwise healthy circuit.

Possible Causes
HighLamp/LED failure within the fixture itself, unrelated to circuit health
HighIsolation transformer failure at that specific location
MedA corroded or loose L-823 connector at that fixture only
MedA secondary cable break inside the base can specific to that fixture
LowA manufacturing defect isolated to that one fixture unit
LowPhysical damage to that specific fixture, such as impact or vibration, not affecting the shared circuit
Required Tools
True-RMS multimeterSpare fixture/lamp/LED moduleSpare isolation transformerBase can access tools
Safety Precautions
  • LOTO before opening the base can even though the primary circuit tests healthy.
Diagnostic Procedure
  1. ObservationConfirm CCR circuit current and overall circuit insulation resistance are both normal, ruling out a shared-circuit cause.
  2. MeasurementTest the isolation transformer output at this specific location.
  3. MeasurementTest the fixture/lamp/LED module directly, bypassing the transformer if needed to isolate the fault further.
  4. DecisionTransformer output normal but fixture dark → fixture/lamp/LED fault. Transformer output abnormal → transformer fault.
  5. Fault LocationConfirm the fault is isolated to this single location's transformer, connector, or fixture.
  6. Root CauseConfirm the replaced component restores normal operation without affecting circuit-level readings.
Test Points
Isolation transformer secondary output at the location
Fixture/lamp/LED module continuity
L-823 connector condition
Secondary cable continuity within the base can
Root Cause Verification

Re-energise and confirm the fixture illuminates correctly, and confirm the overall circuit current remains unchanged, verifying no other unit was affected.

Corrective Action
  • Replace the failed lamp/LED module, transformer, or connector as identified.
Preventive Action
  • Stock spare fixtures/transformers for rapid single-point replacement.
  • Use isolated fixture testing as the default diagnostic starting point whenever circuit-level readings are normal, avoiding unnecessary circuit-wide investigation.
Related References

SOP: SOP-FCS-03 (Field Case Investigation Procedure)

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

Diagram: Base can wiring diagram

Case Study Cross-Reference: Division 08 — Taxiway Centreline / Guidance Lighting Troubleshooting; Division 13 — Secondary Cable Open Circuit (CBL-342)

Rev 0 — Initial issue
FCS-584 Multiple Lights Failure After Cable Work

Symptom — Several fixtures along a section of runway or taxiway went dark within hours of nearby, unrelated cable work being completed by another crew, prompting an investigation into possible collateral damage.

Equipment / System

The primary series circuit cable and joints in the vicinity of the recent cable work, and the group of fixtures downstream of that section.

Possible Causes
HighThe other crew's excavation nicked or stressed the AGL cable without a complete break, causing a delayed-onset fault
HighA joint disturbed during the nearby work was not properly reseated or resealed
MedBackfill compaction near the work site placed mechanical stress on the AGL cable
MedThe other crew's work was not properly coordinated via utility locate, and minor incidental contact went unreported
LowThe timing is coincidental and the fault has an unrelated cause
LowVibration from heavy equipment during the work loosened a nearby connector
Required Tools
TDR / fault locator1000V insulation resistance tester (megger)As-built drawing cross-referenced with the other crew's work permit/locate requestVisual inspection at the work site
Safety Precautions
  • LOTO before any investigation.
  • Coordinate with the other work crew and their supervisor regarding the exact extent and location of their excavation.
Diagnostic Procedure
  1. ObservationMap the affected fixtures and confirm their circuit position downstream of the recent work location.
  2. ObservationObtain the other crew's work permit/locate request and excavation extent for cross-reference.
  3. MeasurementMegger and TDR the circuit section adjacent to the work site.
  4. DecisionFault localised to the work site vicinity → proceed with excavation and repair at that point.
  5. Fault LocationConfirm the specific point of collateral damage.
  6. Root CauseConfirm repair restores all affected fixtures and document the incident against the works coordination record.
Test Points
TDR distance-to-fault relative to the work site
Insulation resistance in segments near the work location
Visual inspection of backfill and cable condition at the site
Root Cause Verification

After repair, confirm all affected fixtures illuminate correctly and megger the section to confirm insulation resistance is restored.

Corrective Action
  • Repair or replace the damaged cable/joint section identified near the work site.
Preventive Action
  • Require a post-work verification test on any AGL circuit near third-party excavation before the work is signed off as complete.
  • Strengthen utility locate and coordination requirements for any work near AGL cable routes.
Related References

SOP: SOP-FCS-04 (Field Case Investigation Procedure), SOP-CBL-22

Standards: FAA AC 150/5340-30

Diagram: Cable route drawing with work site overlay

Case Study Cross-Reference: Division 13 — Cable Damage During Civil Works (CBL-366)

Rev 0 — Initial issue
FCS-585 Transformer Failure After Flooding

Symptom — A cluster of isolation transformers in a low-lying section of the airfield failed simultaneously following a flooding event, with the affected fixtures dark or flickering once floodwater receded and the circuit was re-energised.

Equipment / System

Isolation transformers and their base can enclosures within the flooded area of the affected circuit.

Possible Causes
HighTransformer windings submerged beyond their rated ingress protection, causing internal short circuits or insulation breakdown
HighContaminated floodwater (silt, chemicals) accelerating insulation degradation inside the transformer housing
MedBase can enclosures not rated for the duration/depth of submersion experienced
MedTransformers re-energised before adequate drying and testing, causing secondary damage
LowPhysical debris carried by floodwater damaging transformer connections
LowA design assumption that the location would not flood, now proven incorrect by the event
Required Tools
1000V insulation resistance tester (megger)Moisture detection meterReplacement transformers matched to specificationVisual/physical inspection
Safety Precautions
  • LOTO all affected circuits before any inspection.
  • Treat all submerged transformers as unsafe to energise until fully assessed.
  • Be alert to contamination hazards in floodwater-affected enclosures.
Diagnostic Procedure
  1. ObservationMap the full extent of the flooded area and identify every transformer within it, not just those confirmed failed.
  2. MeasurementMegger every transformer in the flooded zone individually before considering any re-energisation.
  3. MeasurementInspect for contamination and physical damage in addition to simple moisture.
  4. DecisionTransformer insulation resistance acceptable after drying → return to service with continued monitoring. Insulation resistance remains degraded or contamination present → replace the transformer.
  5. Fault LocationIdentify every individual transformer requiring replacement versus those that can be dried and verified.
  6. Root CauseConfirm each transformer is individually verified before restoring the circuit.
Test Points
Individual transformer insulation resistance
Contamination assessment
Base can enclosure condition and seal rating
Root Cause Verification

After replacement/repair, re-megger all affected transformers, re-energise progressively, and monitor closely over the following days for delayed degradation.

Corrective Action
  • Replace transformers that fail insulation testing or show contamination.
  • Dry and re-test transformers with acceptable readings before returning to service.
Preventive Action
  • Review flood risk for low-lying base can locations and consider elevated or better-sealed enclosures.
  • Develop a flood response procedure prioritising critical circuit assessment ahead of routine work.
Related References

SOP: SOP-FCS-05 (Field Case Investigation Procedure), SOP-CBL-23

Standards: IEC 60364, FAA AC 150/5340-30

Diagram: Site drainage and flood risk map

Case Study Cross-Reference: Division 13 — Cable Failure After Flooding (CBL-368)

Rev 0 — Initial issue
FCS-586 Transformer Overheating Under Load

Symptom — A specific isolation transformer was found running noticeably hotter than adjacent transformers under normal operating current, discovered during a routine thermal imaging survey rather than through a light output complaint.

Equipment / System

The specific isolation transformer, its base can enclosure, and its position within the series circuit loading.

Possible Causes
HighInternal winding degradation increasing the transformer's internal resistance and heat generation under normal current
HighThe transformer connected to a fixture drawing higher-than-rated current, such as an incorrect replacement lamp/LED wattage
MedInadequate heat dissipation due to a poorly ventilated or debris-filled base can
MedThe transformer itself undersized or mismatched for the circuit's actual current rating
LowAmbient ground temperature or a nearby heat source elevating the baseline temperature
LowA normal but previously unnoticed operating characteristic for this transformer type, requiring baseline comparison rather than assuming a fault
Required Tools
Thermal imaging cameraClamp ammeterTransformer specification referenceBase can inspection tools
Safety Precautions
  • LOTO before hands-on inspection.
  • Allow the transformer to cool before handling if recently energised.
Diagnostic Procedure
  1. ObservationCompare the thermal reading against adjacent transformers of the same type and loading to establish whether this is a genuine anomaly.
  2. MeasurementMeasure the actual current through the transformer and compare against its rated capacity.
  3. MeasurementInspect the connected fixture to confirm the correct lamp/LED wattage is installed.
  4. DecisionCurrent within rating but transformer still hot → investigate internal winding degradation via insulation/resistance testing. Current above rating → correct the fixture load or transformer sizing.
  5. Fault LocationIsolate to internal winding degradation, an oversized load, or poor heat dissipation.
  6. Root CauseConfirm the temperature returns to a normal comparative range after correction.
Test Points
Thermal image vs. adjacent transformers
Current through the transformer vs. rated capacity
Fixture lamp/LED wattage verification
Base can ventilation/debris condition
Root Cause Verification

Re-thermal-image the transformer under normal load after correction and confirm its temperature is consistent with adjacent units.

Corrective Action
  • Replace a transformer with degraded internal windings.
  • Correct the fixture to the specified lamp/LED wattage.
  • Clear base can ventilation obstruction.
  • Replace with a correctly sized transformer.
Preventive Action
  • Include thermal imaging surveys in the periodic PM cycle rather than relying solely on light-output complaints.
  • Verify replacement lamp/LED specifications against the original design at every service visit.
Related References

SOP: SOP-FCS-06 (Field Case Investigation Procedure)

Standards: IEC 60076 (transformer thermal reference), FAA AC 150/5345-47

Diagram: Base can and transformer specification sheet

Case Study Cross-Reference: Division 13 — Cable Overheating (CBL-360)

Rev 0 — Initial issue
FCS-587 Connector Burning in Series Circuit

Symptom — A primary series circuit connector was found visibly charred or burned during a routine inspection, with the associated fixture still functioning but the connector clearly showing signs of localised overheating and arcing.

Equipment / System

The primary series circuit connector at the affected joint, and the transformer/cable interface it serves.

Possible Causes
HighA high-resistance connection at the connector generating sufficient heat to char the surrounding insulation over time
HighMoisture ingress causing intermittent arcing at the connector contact
MedA connector rated for a lower current than the circuit's actual operating current
MedCorrosion at the connector contact surface increasing resistance progressively
LowA manufacturing defect in the specific connector
LowMechanical stress on the connector from cable movement, causing repeated micro-arcing at a loose contact
Required Tools
Thermal imaging cameraMicro-ohmmeterVisual inspectionReplacement connector kit matched to circuit specification
Safety Precautions
  • LOTO before any work at the burned connector.
  • Treat a burned connector as an active fire/arc-flash risk and do not delay isolation.
  • Use appropriate PPE given potential residual heat or damaged insulation.
Diagnostic Procedure
  1. ObservationDocument the extent of the burning and assess whether it has compromised the surrounding cable insulation beyond the connector itself.
  2. MeasurementThermal image adjacent connectors on the same circuit to determine whether this is an isolated defect or a systemic issue.
  3. MeasurementInspect the connector internals for the specific cause: corrosion, moisture, or a loose/under-crimped contact.
  4. DecisionIsolated defective connector → replace and verify. Pattern found across multiple connectors of the same type/batch → escalate to a circuit-wide inspection and potential connector type replacement program.
  5. Fault LocationConfirm the extent of damage requiring cable repair versus connector-only replacement.
  6. Root CauseConfirm the new connector shows no thermal signature under normal load after replacement.
Test Points
Thermal signature of the replaced connector under load
Adjacent connector thermal survey
Connector resistance via micro-ohmmeter
Cable insulation condition immediately adjacent to the burned connector
Root Cause Verification

Re-thermal-image the repaired connector after a period of normal operation and confirm no recurring hot spot.

Corrective Action
  • Replace the burned connector and any cable insulation compromised by the heat.
  • Address the root cause identified: moisture sealing, correct connector rating, or proper crimp technique.
Preventive Action
  • Include thermal imaging of accessible connectors in the periodic PM cycle.
  • Standardise on connectors correctly rated for the circuit's operating current.
  • Investigate any connector batch showing a repeat pattern of failure.
Related References

SOP: SOP-FCS-07 (Field Case Investigation Procedure), SOP-CBL-14

Standards: IEC 60502, FAA AC 150/5345-26

Diagram: Connector specification and circuit current rating reference

Case Study Cross-Reference: Division 13 — High Resistance Joint (CBL-355)

Rev 0 — Initial issue
FCS-588 Cable Insulation Failure Underground

Symptom — A buried section of primary series cable was identified as having failed insulation resistance during a routine periodic test, with no visible surface indication and no reported operational fault at the time of discovery.

Equipment / System

The buried cable section identified by the periodic insulation resistance test, prior to any excavation or visual confirmation.

Possible Causes
HighLong-term cumulative ageing of the cable insulation reaching end of service life
HighAn undiscovered installation-era defect (nick, substandard joint) that has progressively worsened over years of burial
MedLocalised soil chemistry or moisture conditions accelerating degradation in that specific section
MedA previously unreported mechanical disturbance, such as root growth or ground settlement, affecting the buried cable
LowRodent damage at a point not yet manifesting as a visible surface issue
LowA testing or measurement error requiring confirmation before committing to excavation
Required Tools
1000V/2500V insulation resistance tester (megger)TDR / fault locatorAs-built drawingExcavation equipment
Safety Precautions
  • LOTO before testing.
  • Coordinate utility locate before any excavation is planned.
Diagnostic Procedure
  1. ObservationConfirm the failed reading through a repeat test with calibrated equipment to rule out a measurement error.
  2. MeasurementSegment the circuit to narrow down the specific section responsible for the low reading.
  3. MeasurementUse TDR to estimate the fault location within the identified segment before committing to excavation extent.
  4. DecisionReading confirmed and localised → proceed with targeted excavation and repair. Reading marginal and not clearly localised → continue monitoring with more frequent testing before excavating.
  5. Fault LocationConfirm the precise excavation point using TDR and, where needed, a secondary locating method.
  6. Root CauseUpon excavation, visually confirm the actual defect matches the electrical signature predicted.
Test Points
Segment insulation resistance
TDR distance-to-fault
Visual condition of the cable upon excavation
Root Cause Verification

After repair, megger the full loop and confirm the reading is restored to, or above, the acceptable threshold, then continue periodic monitoring.

Corrective Action
  • Repair or replace the identified buried cable section.
Preventive Action
  • Schedule periodic insulation resistance testing on a defined interval for all buried circuits, rather than relying on operational faults to reveal ageing insulation.
  • Prioritise proactive replacement of circuit sections approaching known end-of-life age.
Related References

SOP: SOP-FCS-08 (Field Case Investigation Procedure), SOP-CBL-05

Standards: IEC 60364, FAA AC 150/5340-30

Diagram: Circuit route drawing with installation dates

Case Study Cross-Reference: Division 13 — Cable Insulation Failure (CBL-345); Division 13 — Hidden Underground Cable Fault (CBL-370)

Rev 0 — Initial issue
FCS-589 Intermittent Earth Fault

Symptom — A circuit's earth-fault monitoring showed repeated, brief trip events that cleared on their own or on a simple reset, with no fault found during standard testing performed shortly after each event, making the condition difficult to pin down over several weeks.

Equipment / System

The full primary series circuit, evaluated for a fault condition present only intermittently rather than continuously.

Possible Causes
HighA marginal insulation defect that only becomes conductive under specific conditions (temperature, vibration, moisture) not present at the time of routine testing
HighA loose or partially broken conductor making and breaking contact under vibration from aircraft/ground traffic
MedA connector with thermal-cycling-dependent contact, closing the fault path only at a certain temperature
MedA nearby source of electrical interference, or a genuinely marginal CCR earth-fault relay setting, causing some events to be false positives mixed with real ones
LowWildlife activity, such as chewing or nesting, causing an intermittent contact at unpredictable times
LowA fault correlated with a specific, infrequent operational condition, such as only at maximum intensity or during specific weather, not yet identified
Required Tools
CCR earth-fault trend log with timestamps1000V insulation resistance tester (megger)Continuous monitoring/data-logging equipmentWeather and operational condition correlation data
Safety Precautions
  • LOTO before any hands-on testing.
  • Treat an intermittent fault as an ongoing hazard even between events.
Diagnostic Procedure
  1. ObservationCompile a detailed timeline of every trip event with exact timestamp, and cross-reference against weather, temperature, and CCR intensity step at the time.
  2. MeasurementInstall temporary continuous monitoring/data-logging equipment on the circuit to capture conditions at the moment of the next event, since standard spot-testing after the fact has proven insufficient.
  3. MeasurementOnce a correlating condition is identified, attempt to reproduce it under controlled testing, such as testing at maximum intensity or physically flexing suspect connectors.
  4. DecisionA condition is successfully correlated and reproduced → proceed to isolate the specific component responsible under that condition. No clear correlation after extended monitoring → broaden the investigation to a full segment-by-segment stress test.
  5. Fault LocationIsolate to the specific component or condition-dependent defect once reproducible.
  6. Root CauseConfirm the fault no longer occurs under the previously identified triggering condition after repair.
Test Points
Timestamped trip log correlated with weather/temperature/intensity
Continuous monitoring data capturing conditions at the moment of fault
Reproducibility of the fault under controlled test conditions
Root Cause Verification

Monitor the circuit over an extended period covering the range of previously implicated conditions and confirm no further trip events occur.

Corrective Action
  • Repair or replace the specific component identified as condition-dependent, such as a loose conductor, a thermally sensitive connector, or a marginal insulation defect.
  • Adjust CCR earth-fault relay sensitivity only if a false-positive component of the pattern is confirmed and remains within acceptable safety limits.
Preventive Action
  • Install permanent trend-logging with sufficient resolution to capture intermittent events on circuits with any history of unexplained trips.
  • Treat repeated 'no fault found' results after a trip event as a signal to escalate to continuous monitoring rather than closing out the investigation.
Related References

SOP: SOP-FCS-09 (Field Case Investigation Procedure)

Standards: IEC 60364, FAA AC 150/5340-30

Diagram: Circuit route drawing with trip event log overlay

Case Study Cross-Reference: Division 13 — Cable Earth Fault (CBL-344); Division 13 — Repeated Cable Fault (CBL-369)

Rev 0 — Initial issue
FCS-590 Repeated LED Fixture Failure

Symptom — The same model of LED fixture failed repeatedly across multiple locations on the airfield well before its expected service life, prompting an investigation into whether the cause was fixture design, environmental conditions, or installation practice.

Equipment / System

The specific LED fixture model and its driver, evaluated across multiple failed units to identify a common failure pattern.

Possible Causes
HighA systemic LED driver design weakness, such as inadequate surge protection or thermal management, affecting the whole batch/model
HighA mismatch between the fixture's environmental rating and the airfield's actual operating conditions (temperature extremes, moisture exposure)
MedA common installation practice error repeated across all affected locations, such as incorrect torque or moisture entry at a specific gasket
MedA specific batch/lot of fixtures with a manufacturing defect, distinct from the model as a whole
LowA power quality issue (voltage transients, harmonics) on the circuits feeding these fixtures common to all failures
LowCoincidental unrelated failures being incorrectly grouped as a pattern
Required Tools
Failed unit collection and bench-testing setupLED driver diagnostic toolPower quality loggerManufacturer failure analysis support/RMA process
Safety Precautions
  • LOTO before removing any failed unit.
  • Follow manufacturer guidance for handling failed LED drivers, which may retain stored energy in capacitors.
Diagnostic Procedure
  1. ObservationCompile failure data across all affected locations: installation date, failure date, location/environment, and circuit.
  2. MeasurementBench-test a sample of failed units to identify the specific internal failure mode: driver component, LED array, or thermal damage.
  3. MeasurementCheck power quality on the circuits feeding the affected fixtures for any common transient or harmonic issue.
  4. DecisionCommon internal failure mode across units → escalate to the manufacturer as a design/batch issue and request failure analysis. Failure mode varies with no common pattern → treat as installation practice at each site individually.
  5. Fault LocationIdentify whether the failure pattern points to the fixture design, a specific batch, installation practice, or circuit power quality.
  6. Root CauseConfirm the corrective action — replacement fixture, corrected installation practice, or power quality correction — eliminates the recurrence.
Test Points
Bench-test failure mode analysis across a sample of failed units
Power quality measurement at affected circuits
Installation records (date, method, technician) for affected locations
Environmental exposure comparison between failed and non-failed units of the same model
Root Cause Verification

Monitor the replacement fixtures, or the corrected installation, over an extended period, at least matching the previous failures' typical time-to-failure, and confirm no recurrence.

Corrective Action
  • Replace affected fixtures with a corrected design/batch per manufacturer guidance.
  • Correct the identified installation practice.
  • Address a power quality issue at its source.
Preventive Action
  • Maintain a fixture failure log by model and batch to detect emerging patterns early.
  • Engage the manufacturer proactively when a repeat failure pattern is first suspected rather than after many units have failed.
  • Verify environmental rating suitability before standardising on a fixture model for airfield use.
Related References

SOP: SOP-FCS-10 (Field Case Investigation Procedure)

Standards: FAA AC 150/5345-46 (LED fixture specification), IEC 62031

Diagram: Fixture failure log and location map

Case Study Cross-Reference: Division 08 — Taxiway Centreline / Guidance Lighting Troubleshooting; Division 11 — PAPI LED Failure (PAPI-300)

Rev 0 — Initial issue
FCS-591 Sign Board Partial Illumination

Symptom — An internally illuminated airfield sign was found with only part of its legend or background illuminated, with some segments dark while others remained lit, making the sign's message unclear or misleading.

Equipment / System

Internally illuminated sign panel, its internal light source (LED array or LED panel), and the associated ballast/driver.

Possible Causes
HighPartial failure of an LED array serving only part of the sign panel
HighA driver serving one section of the sign failed while a separate driver for another section remains functional
MedA physical partition or reflector issue within the sign causing uneven light distribution even with a functioning source
MedA wiring fault to one specific portion of the internal lighting
LowA partially failed connector affecting only part of the internal circuit
LowSign panel damage, such as a cracked or delaminated face, reducing apparent illumination in one area without an actual electrical fault
Required Tools
True-RMS multimeterSign panel access toolsSpare LED array/driver matched to sign typeVisual inspection light
Safety Precautions
  • LOTO before opening the sign housing.
  • Treat mandatory instruction signs as operationally critical given their role in preventing runway incursions, and prioritise repair accordingly.
Diagnostic Procedure
  1. ObservationDocument exactly which portion of the sign is dark and correlate with the sign's internal lighting zone layout.
  2. MeasurementWith the housing open and circuit isolated, test each internal lighting zone/driver independently.
  3. MeasurementInspect the sign face and internal reflectors for physical damage separate from the electrical fault.
  4. DecisionSpecific zone's source/driver confirmed faulty → replace that component. Physical panel damage found → assess for panel replacement in addition to any electrical repair.
  5. Fault LocationIsolate to the specific internal zone, source, driver, or panel defect.
  6. Root CauseConfirm uniform illumination across the full sign face after repair.
Test Points
Individual internal lighting zone output
Driver function per zone
Wiring continuity to the affected zone
Physical panel condition
Root Cause Verification

Re-energise and visually confirm uniform, full illumination of the sign legend and background at night before closing out.

Corrective Action
  • Replace the failed LED array or driver for the affected zone.
  • Repair the wiring fault.
  • Replace a damaged sign panel.
Preventive Action
  • Include full-panel illumination verification, not just 'sign is lit', in the periodic PM cycle.
  • Stock spare components matched to each sign type/generation in use on the airfield.
Related References

SOP: SOP-FCS-11 (Field Case Investigation Procedure)

Standards: FAA AC 150/5345-44 (Specification for Runway and Taxiway Signs), ICAO Annex 14 Vol I

Diagram: Sign panel internal wiring/zone layout diagram

Case Study Cross-Reference: Division 07 — Taxiway Light Troubleshooting; Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue
FCS-592 PAPI Incorrect Indication

Symptom — Multiple independent pilot reports over several weeks indicated the PAPI on one runway occasionally showed an indication inconsistent with the aircraft's actual glide path, though the PAPI passed a standard visual inspection and basic angle check each time it was investigated during daylight.

Equipment / System

PAPI wing bar, evaluated for a condition that might only manifest under specific conditions (time of day, sun angle, temperature) not present during standard daytime inspection.

Possible Causes
HighA sun-angle-dependent optical interference, such as solar glare through the lens at specific times of day, creating a false indication under particular lighting conditions
HighA marginal elevation angle error only detectable with precision survey equipment, not a basic visual check
MedThermal expansion/contraction of the mounting structure causing a small angle drift at certain temperatures that resolves by the time of daytime inspection
MedA specific unit's red filter with a marginal defect that only manifests at certain ambient light levels
LowReports correlate with a specific time of day suggesting an external light source, such as vehicle headlights, creating a false indication rather than a PAPI fault
LowReports are pilot perception variance rather than an actual system fault, requiring careful correlation before concluding a hardware cause
Required Tools
Collimating theodolite / PAPI angle test setPrecise timestamp log of pilot reports cross-referenced with sun position/weather dataThermal imaging cameraRed filter transmittance reference
Safety Precautions
  • Notify airfield operations of the ongoing investigation.
  • Consider a temporary operational note if a pattern is confirmed pending full resolution.
  • LOTO before any physical adjustment.
Diagnostic Procedure
  1. ObservationCompile all pilot reports with precise time, date, and approach direction, and cross-reference against sun position and weather at each reported time.
  2. MeasurementConduct the angle survey specifically at the time of day correlating with the reports, rather than only during standard daytime hours.
  3. MeasurementInspect for solar glare interference by observing the PAPI from the approach path at the correlating time and sun angle.
  4. DecisionAngle survey at the correlating time reveals a drift not present at other times → investigate thermal/structural cause. Solar glare confirmed → assess for a physical shading/baffle solution or unit relocation.
  5. Fault LocationIsolate the cause to a specific time-dependent condition affecting the wing bar or a specific unit.
  6. Root CauseConfirm the corrective action eliminates the indication issue by verifying at the previously correlating time/conditions.
Test Points
Angle survey conducted at the time-of-day correlating with reports
Solar glare observation from the approach path
Thermal imaging of the mounting structure across a full day/temperature cycle
Red filter transmittance under varying ambient light
Root Cause Verification

Monitor for further pilot reports over an extended period covering the previously correlating conditions and confirm no recurrence, supplemented by a follow-up survey at the same time of day.

Corrective Action
  • Apply the applicable Division 11 corrective action once the specific time-dependent cause is identified: angle correction, filter replacement, or a physical glare mitigation.
Preventive Action
  • When investigating an intermittent PAPI report, always attempt to replicate the survey conditions (time, sun angle, temperature) rather than relying solely on standard daytime inspection.
  • Maintain a pilot report log correlated with environmental conditions for pattern recognition.
Related References

SOP: SOP-FCS-12 (Field Case Investigation Procedure), Division 11 procedures

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

Diagram: PAPI site diagram with sun path overlay

Case Study Cross-Reference: Division 11 — PAPI/VASI Troubleshooting

Rev 0 — Initial issue
FCS-593 Approach Light Photometry Failure

Symptom — A photometric survey flight of the approach lighting system returned intensity readings below the required minimum for several units, even though those units appeared to operate normally during a standard ground inspection and passed a basic visual check at night.

Equipment / System

Approach lighting system units flagged by the photometric survey, evaluated for the specific parameter (intensity, colour, or beam pattern) that failed.

Possible Causes
HighGradual lamp/LED lumen depreciation below the specified minimum, not obvious to the naked eye during a routine visual check
HighLens/filter contamination reducing transmittance without being visually obvious in daylight or from ground level
MedA beam alignment drift causing the peak intensity to be measured off-axis from where the survey aircraft sampled it
MedThe survey itself conducted under marginal conditions, such as atmospheric haze or equipment calibration drift, requiring cross-verification
LowA driver/transformer output drift reducing intensity without a complete failure
LowA data recording or unit-identification error in the survey report itself
Required Tools
Calibrated ground photometer/luminance meterColour coordinate/chromaticity meterSurvey report and flight dataLens cleaning kitAlignment verification tools
Safety Precautions
  • LOTO before any component-level correction.
  • Coordinate ground-based re-measurement with airfield operations if it requires access near the approach lighting array.
Diagnostic Procedure
  1. ObservationReview the photometric survey report to identify exactly which units and which parameter failed, and cross-check the survey conditions (weather, equipment calibration) for validity.
  2. MeasurementRe-verify the flagged units' output with a calibrated ground photometer under controlled conditions to confirm the survey finding independent of the flight measurement.
  3. MeasurementInspect the flagged units for lens contamination, alignment, and driver output.
  4. DecisionGround re-measurement confirms the shortfall → proceed with the applicable corrective action (cleaning, alignment, or component replacement). Ground re-measurement finds units within specification → investigate the survey's validity rather than the units themselves.
  5. Fault LocationIsolate the cause to lens contamination, alignment drift, driver output, or a survey data issue.
  6. Root CauseConfirm restored compliance with a repeat ground measurement and, where required by the applicable standard, a follow-up flight survey.
Test Points
Ground photometer reading vs. ICAO/FAA minimum for each flagged unit
Chromaticity coordinates
Beam alignment vs. specification
Survey equipment calibration record and conditions at time of survey
Root Cause Verification

Repeat the ground measurement after correction and confirm compliance, then schedule the next flight survey to confirm resolution from the air.

Corrective Action
  • Clean or replace the lens/filter assembly.
  • Realign the unit.
  • Replace or recalibrate the driver/transformer.
  • Correct a survey data/identification error where the units themselves are confirmed compliant.
Preventive Action
  • Schedule ground-based photometric spot checks between flight surveys to catch gradual drift earlier.
  • Include lens cleaning in the routine PM cycle ahead of each scheduled flight survey.
Related References

SOP: SOP-FCS-13 (Field Case Investigation Procedure), Division 26 procedures

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

Diagram: Approach lighting photometric survey report and unit layout

Case Study Cross-Reference: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue
FCS-594 Runway Edge Light Alignment Failure

Symptom — A pilot report during a crosswind landing noted that a section of runway edge lights appeared to lean or was less visible from certain approach angles, and a follow-up ground inspection found several edge light fixtures tilted out of vertical alignment.

Equipment / System

Runway edge light fixtures and their mounting bases/frangible couplings along the affected section.

Possible Causes
HighGround settlement or frost heave beneath the fixture bases causing gradual tilt over time
HighVehicle or snow plough contact disturbing the frangible mounting without triggering a complete break
MedFrangible coupling degraded or improperly torqued at installation, allowing gradual drift under wind loading
MedA previous repair not fully re-levelling the fixture after replacement
LowThe base can/foundation itself settled or shifted, affecting multiple fixtures in a localised area
LowThe pilot report reflects a normal visual perspective effect rather than an actual misalignment, requiring verification before assuming a fault
Required Tools
Precision level/inclinometerTorque wrench for frangible coupling hardwareSite survey referenceVisual inspection
Safety Precautions
  • LOTO before adjustment.
  • Coordinate airside access.
  • Use appropriate care when working near frangible couplings designed to break away under specific loads.
Diagnostic Procedure
  1. ObservationConduct a ground-level visual and instrument survey of the reported section to confirm the extent and degree of tilt across all fixtures in the area.
  2. MeasurementMeasure each fixture's vertical alignment against the specification tolerance using a precision level.
  3. MeasurementInspect the frangible coupling and base for looseness, damage, or foundation settlement.
  4. DecisionLooseness/coupling issue → re-torque or replace the coupling and re-level the fixture. Foundation settlement → address the underlying foundation issue in addition to re-levelling.
  5. Fault LocationConfirm the extent of fixtures affected and the specific mechanical cause.
  6. Root CauseConfirm all fixtures are re-levelled within tolerance after correction.
Test Points
Vertical alignment per fixture vs. specification tolerance
Frangible coupling torque and condition
Foundation/base level
Root Cause Verification

Re-survey the corrected fixtures and confirm alignment holds after a subsequent period, particularly following any high-wind or freeze-thaw event.

Corrective Action
  • Re-level and re-torque the frangible coupling on each affected fixture.
  • Address foundation settlement where confirmed as the cause.
Preventive Action
  • Include fixture vertical alignment checks in the periodic PM cycle, not just illumination status.
  • Investigate any area with known settlement history more frequently.
Related References

SOP: SOP-FCS-14 (Field Case Investigation Procedure)

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

Diagram: Runway edge light mounting and frangible coupling detail drawing

Case Study Cross-Reference: Division 05 — Runway Centreline Light Troubleshooting

Rev 0 — Initial issue
FCS-595 Taxiway Light Water Ingress

Symptom — A taxiway edge or centreline fixture was found with condensation or standing water inside its housing during a routine inspection, discovered before any electrical fault had yet occurred, prompting an investigation into how widespread the issue might be across similar fixtures.

Equipment / System

Taxiway light fixture housing, lens gasket, and cable entry point, along with a review of similar fixtures across the airfield of the same type/installation batch.

Possible Causes
HighA degraded lens gasket allowing water entry, consistent with the fixture's age or a known gasket material issue
HighA cable entry gland not properly sealed at installation or a previous service visit
MedA fixture design with a marginal drainage provision under heavy rainfall conditions
MedA fixture that was accessed for other maintenance and not properly resealed afterward
LowA cracked housing from a vehicle strike or snow plough contact not otherwise reported
LowCondensation from normal thermal cycling in a poorly ventilated but otherwise sealed housing, distinct from an external ingress point
Required Tools
Moisture detection meter1000V insulation resistance tester (megger)Replacement gasket kitCable gland sealantFixture maintenance history log
Safety Precautions
  • LOTO before opening any fixture suspected of water ingress.
  • Treat wet internal components as live until insulation resistance is verified.
Diagnostic Procedure
  1. ObservationConfirm the extent of moisture/water within this specific fixture and check the fixture's maintenance history for a recent service visit that may not have been properly resealed.
  2. MeasurementMegger the fixture's internal wiring before considering any re-energisation.
  3. MeasurementInspect the lens gasket and cable gland for the specific entry point.
  4. DecisionInsulation resistance acceptable → dry out, reseal, and return to service. Insulation resistance degraded → treat as a component-level fault requiring replacement.
  5. Fault LocationIsolate the specific seal or gland responsible for the entry point.
  6. Root CauseConfirm the fixture is fully dry and resealed, then check a sample of similar fixtures across the airfield to assess whether this is an isolated case or a wider batch/design issue.
Test Points
Insulation resistance before re-energisation
Lens gasket and cable gland seal condition
Comparative check of similar fixtures of the same type/installation batch
Root Cause Verification

After drying and resealing, re-megger, re-energise, and monitor through the next several rainfall events; if a batch pattern is found, extend monitoring to all fixtures of that type.

Corrective Action
  • Replace the degraded gasket.
  • Reseal the cable gland.
  • Repair a cracked housing.
Preventive Action
  • Include gasket condition and seal inspection in the periodic PM cycle, particularly for older fixture installations.
  • Verify proper resealing as a mandatory step after any fixture access.
Related References

SOP: SOP-FCS-15 (Field Case Investigation Procedure), SOP-CBL-11

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

Diagram: Taxiway fixture housing and seal detail drawing

Case Study Cross-Reference: Division 07 — Taxiway Light Troubleshooting; Division 13 — Cable Water Ingress (CBL-352)

Rev 0 — Initial issue
FCS-596 Stop Bar Control Failure

Symptom — During a routine LVP readiness drill, not an actual low-visibility event, a stop bar at one runway-holding position failed to respond when commanded off from the tower, remaining illuminated after the taxiway centreline lead-on lights had already activated, creating a conflicting indication.

Equipment / System

Stop bar control relay/switching module and its communication link to the tower/ALCMS, discovered during a proactive drill rather than an actual operational event.

Possible Causes
HighA control relay or switching module partially failed, sticking in the 'on' state despite receiving the 'off' command
HighA communication fault between the tower control system and the local controller specific to this holding position
MedA software/configuration issue in the ALCMS specific to this stop bar's addressing
MedThe interlock logic between the stop bar and the taxiway centreline lead-on lights malfunctioning, causing the observed conflict
LowThe drill itself was conducted incorrectly, and the stop bar was never actually commanded off
LowA wiring fault between the relay and the physical stop bar fixtures
Required Tools
ALCMS/tower stop bar control panelTrue-RMS multimeterControl relay/switching module diagnostic toolStop bar and interlock circuit diagram
Safety Precautions
  • Treat the finding with the same urgency as an actual operational failure, since the drill successfully caught a fault that would otherwise have manifested during a real LVP event.
  • LOTO before corrective work.
Diagnostic Procedure
  1. ObservationConfirm the drill command sequence was executed correctly by reviewing the tower control log.
  2. MeasurementVerify the command signal reaching the stop bar's local controller.
  3. MeasurementCheck the control relay/switching module and the interlock logic between the stop bar and the lead-on lights.
  4. DecisionCommand signal correct but stop bar unresponsive → local relay/switching module fault. Command signal not reaching the controller → communication/configuration fault.
  5. Fault LocationConfirm the specific point of failure.
  6. Root CauseConfirm the stop bar responds correctly to repeated on/off commands during a follow-up drill before considering the holding position ready for LVP service.
Test Points
Tower/ALCMS command signal to the stop bar
Control relay/switching module status
Interlock logic between stop bar and lead-on lights
Wiring continuity to the physical fixtures
Root Cause Verification

Repeat the LVP readiness drill at this holding position multiple times and confirm consistent, correct response before closing out.

Corrective Action
  • Replace the failed control relay or switching module.
  • Repair the communication link.
  • Correct the ALCMS addressing/configuration.
  • Correct the interlock logic.
Preventive Action
  • Conduct regular LVP readiness drills at all holding positions rather than relying solely on actual low-visibility events to reveal a fault.
  • Treat drill findings with the same corrective priority as an operational fault, since a drill's purpose is to find faults before they matter operationally.
Related References

SOP: SOP-FCS-16 (Field Case Investigation Procedure), SOP-LVO-06

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, ICAO Doc 9365

Diagram: Stop bar control and interlock circuit diagram

Case Study Cross-Reference: Division 20 — Stop Bar Failure During LVO (LVO-497)

Rev 0 — Initial issue
FCS-597 ALCMS Communication Failure

Symptom — The central ALCMS monitoring station intermittently lost communication with a group of field controllers serving one section of the airfield, with the status display showing stale or unknown data for that section for several minutes at a time before self-recovering, without any confirmed underlying lighting fault.

Equipment / System

The communication network segment (fibre, copper, or wireless link) serving the affected field controllers, and the ALCMS central server's handling of the intermittent link.

Possible Causes
HighA degrading physical link, such as a fibre connector or copper splice, in the affected segment causing intermittent signal loss
HighA network switch or media converter hardware nearing failure at a point along the segment
MedElectromagnetic interference from a nearby source affecting the specific segment intermittently
MedA software/firmware issue in the field controllers or central server causing periodic communication drops unrelated to the physical link
LowNetwork congestion or a configuration issue causing periodic timeouts
LowA power quality issue at an intermediate network component causing brief resets
Required Tools
Network diagnostic tools (ping, traceroute, link quality/error rate monitoring)Fibre/cable test equipmentALCMS server and field controller logsSpare network hardware
Safety Precautions
  • LOTO before hands-on work on network infrastructure.
  • Coordinate with airfield operations regarding the reduced monitoring visibility during the investigation.
Diagnostic Procedure
  1. ObservationReview the ALCMS and network logs to establish the precise pattern and timing of the communication drops.
  2. MeasurementMonitor link quality/error rate continuously on the affected segment to catch the condition in the act rather than relying on the intermittent symptom alone.
  3. MeasurementPhysically inspect and test connectors, splices, and intermediate hardware along the segment.
  4. DecisionLink quality data shows a physical-layer error pattern correlating with the drops → proceed to physical link repair. No physical-layer correlation → investigate field controller/server software or configuration.
  5. Fault LocationIsolate to the specific physical link, hardware component, or software/configuration issue.
  6. Root CauseConfirm sustained, error-free communication over an extended monitoring period after correction.
Test Points
Continuous link quality/error rate monitoring
Physical connector/splice/hardware inspection
Field controller and ALCMS server logs correlated with drop events
Root Cause Verification

Monitor the repaired segment continuously for an extended period, at least matching the previous typical time between drop events, and confirm no recurrence.

Corrective Action
  • Repair or replace the degraded physical link component.
  • Replace failing network hardware.
  • Update firmware/software where a non-physical cause is confirmed.
  • Correct a configuration issue.
Preventive Action
  • Implement continuous link quality monitoring with alerting for degrading trends, rather than waiting for a full communication loss to investigate.
  • Include network infrastructure inspection in the periodic PM cycle.
Related References

SOP: SOP-FCS-17 (Field Case Investigation Procedure), SOP-LVO-07

Standards: ALCMS/monitoring system technical manual, relevant network cabling standards

Diagram: ALCMS network architecture diagram with the affected segment highlighted

Case Study Cross-Reference: Division 20 — AGL Monitoring Failure During LVO (LVO-500)

Rev 0 — Initial issue
FCS-598 Remote CCR Control Failure

Symptom — A CCR failed to respond to a remote intensity step command sent from the ALCMS, remaining at its previous intensity setting despite the ALCMS interface showing the command as successfully sent, discovered when tower personnel reported the runway lights had not brightened as expected during a visibility-reducing weather change.

Equipment / System

The CCR's remote control interface/communication module and its link to the ALCMS, distinct from the CCR's power regulation function itself, which continued operating normally at the previous setting.

Possible Causes
HighThe CCR's remote control communication module failed while the CCR's core regulation function remained healthy
HighA communication link fault between the ALCMS and this specific CCR, distinct from other CCRs on the same network that responded correctly
MedThe CCR was in local/manual control mode rather than remote mode, either due to a switch left in the wrong position after previous maintenance or an operator error
MedA command addressing error in the ALCMS sent the command to the wrong CCR or with an invalid step value
LowA power supply issue to the CCR's control module distinct from its main power circuit
LowA software/firmware fault in the CCR's control module
Required Tools
ALCMS command logCCR local control panelCommunication link diagnostic toolsCCR technical manual
Safety Precautions
  • LOTO before hands-on work on the CCR control module.
  • Be aware the CCR's main power circuit may remain live and energised even while investigating the control module fault.
Diagnostic Procedure
  1. ObservationConfirm via the ALCMS command log exactly what command was sent and to which CCR, and cross-check against the CCR's actual local status.
  2. MeasurementCheck the CCR's local/remote control mode switch position.
  3. MeasurementTest the communication link specifically to this CCR, comparing against other CCRs on the same network segment that responded correctly.
  4. DecisionCCR found in local mode → switch to remote and verify. Communication link fault isolated to this CCR → investigate its specific control module/link.
  5. Fault LocationConfirm the specific point of failure: mode switch, control module, or communication link.
  6. Root CauseConfirm the CCR responds correctly to a test remote command before considering the fault resolved.
Test Points
CCR local/remote mode switch position
Communication link status specific to this CCR
ALCMS command log accuracy
CCR control module power/status
Root Cause Verification

Send a series of test remote commands across multiple intensity steps and confirm the CCR responds correctly each time before closing out.

Corrective Action
  • Switch the CCR to remote mode if found incorrectly set to local.
  • Repair or replace the CCR's communication module.
  • Repair the communication link.
  • Correct an ALCMS addressing error.
Preventive Action
  • Verify remote/local mode switch position is returned to remote as a mandatory step after any local maintenance on a CCR.
  • Include a remote command response test in the periodic PM cycle for all CCRs.
Related References

SOP: SOP-FCS-18 (Field Case Investigation Procedure), SOP-LVO-07

Standards: ALCMS/monitoring system technical manual, CCR technical manual

Diagram: CCR remote control interface and network diagram

Case Study Cross-Reference: Division 01 — CCR Troubleshooting; Division 20 — AGL Monitoring Failure During LVO (LVO-500)

Rev 0 — Initial issue
FCS-599 Photometry Measurement Discrepancy

Symptom — Two photometric measurements of the same runway lighting system, taken only weeks apart using different measurement methods (a flight survey and a ground-based spot check), produced significantly different intensity results for several of the same units, creating uncertainty about the system's true compliance status.

Equipment / System

The specific units showing discrepant readings, along with both measurement systems (flight survey equipment and ground photometer) used to assess them.

Possible Causes
HighA difference in measurement geometry between the flight survey and the ground spot check, producing genuinely different but individually valid readings for a unit with an asymmetric beam pattern
HighCalibration drift in one of the two measurement systems since its last calibration
MedEnvironmental conditions, such as temperature or atmospheric haze, differing significantly between the two measurement occasions
MedThe units' actual output changed between the two measurement dates due to a real but gradual degradation, meaning both readings could be accurate for their respective times
LowA data recording or unit-identification error causing a mismatch between which physical unit corresponds to which reading in one of the two data sets
LowA genuine, confirmed hardware fault causing highly variable output, distinct from a measurement methodology difference
Required Tools
Both measurement systems' calibration recordsA third independent ground measurement for tie-breakingMeasurement geometry/angle documentation for both surveysUnit identification cross-reference
Safety Precautions
  • LOTO before any hands-on unit inspection.
  • Treat the compliance status as unresolved and exercise appropriate caution regarding any category-critical implications until the discrepancy is understood.
Diagnostic Procedure
  1. ObservationCompile the exact measurement geometry, conditions, and calibration status for both original measurements to identify whether a methodology difference alone could explain the discrepancy.
  2. MeasurementConduct a third, independent ground measurement using freshly calibrated equipment at a controlled, standard measurement geometry to serve as a tie-breaker.
  3. MeasurementVerify unit identification consistency across all three data sets to rule out a data-matching error.
  4. DecisionThird measurement aligns with one of the original two → investigate why the other original measurement was in error. Third measurement falls between the two originals or reveals genuine variability → investigate the units themselves for an intermittent or condition-dependent fault.
  5. Fault LocationIsolate the discrepancy to a measurement methodology/calibration issue or a genuine unit-level fault.
  6. Root CauseConfirm a consistent, repeatable reading for the affected units using a standardised measurement approach going forward.
Test Points
Measurement geometry and conditions for each survey
Calibration records for both measurement systems
A controlled tie-breaker measurement
Unit identification cross-reference across all data sets
Root Cause Verification

Establish a standardised measurement protocol (geometry, conditions, calibration interval) for future surveys of this system and confirm consistent results are obtained going forward.

Corrective Action
  • Recalibrate the measurement system found to be in error.
  • Correct a unit-identification/data-matching error.
  • If a genuine unit-level fault is confirmed, apply the applicable corrective action per the relevant division procedure.
Preventive Action
  • Standardise measurement geometry and conditions across all photometric survey methods used for the same system to enable meaningful comparison.
  • Maintain rigorous calibration schedules for all measurement equipment and document calibration status with every survey result.
Related References

SOP: SOP-FCS-19 (Field Case Investigation Procedure)

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

Diagram: Measurement geometry comparison diagram for both survey methods

Case Study Cross-Reference: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue
FCS-600 Recurring Airport AGL Failure RCA

Symptom — Over a period of several months, the same general category of AGL fault recurred across multiple, seemingly unrelated locations at a frequency well above the airfield's historical baseline, prompting a formal root cause analysis (RCA) at the airfield-system level rather than treating each occurrence as an isolated repair.

Equipment / System

The full population of AGL systems/circuits exhibiting the elevated fault rate, evaluated collectively rather than as individual repairs, alongside the maintenance and fault history records for the airfield.

Possible Causes
HighA common installation-era defect, such as a specific cable batch, joint kit, or fixture model, affecting many locations now reaching a similar point in their service life simultaneously
HighA systemic environmental change, such as a shift in groundwater conditions, increased traffic loading, or a new nearby construction project, affecting multiple circuits similarly
MedA maintenance practice or spare parts substitution introduced airfield-wide around the time the elevated fault rate began
MedA broader infrastructure ageing effect coinciding across many circuits installed in the same era, rather than any single distinct cause
LowA change in fault detection/reporting sensitivity, such as a new monitoring system, revealing faults that previously went unnoticed rather than a genuine increase in the underlying fault rate
LowA genuinely coincidental clustering of unrelated individual faults, requiring statistical analysis to distinguish from a true systemic pattern
Required Tools
Full fault history database/log across the affected periodInstallation records (dates, batches, contractors) for affected locationsStatistical trend analysisRoot cause analysis framework (5-Why, fishbone/Ishikawa diagram)
Safety Precautions
  • Coordinate with airfield operations regarding the scope and priority of the RCA given its airfield-wide implications.
  • Continue standard LOTO and safety procedures for any individual fault investigation conducted as part of the RCA.
Diagnostic Procedure
  1. ObservationCompile the complete fault history for the affected category over an extended period and establish the actual baseline fault rate for comparison, confirming the increase is statistically real rather than a perception.
  2. ObservationMap all affected locations against installation date, contractor, material batch, and any common maintenance history.
  3. MeasurementConduct detailed investigation of a representative sample of the recurring faults using the applicable division-specific diagnostic procedure for each, looking for a common failure mode across the sample.
  4. MeasurementCorrelate the onset of the elevated fault rate against any known change: installation era, maintenance practice, environmental shift, or monitoring system change.
  5. DecisionA common cause is identified across the sample → scope the full extent of at-risk locations sharing that common factor for proactive action. No common cause identified beyond general ageing → treat as an infrastructure life-cycle issue requiring a broader replacement/renewal program.
  6. Fault LocationDefine the full population of locations sharing the identified common cause.
  7. Root CauseConfirm the identified cause explains the pattern by testing the hypothesis against locations that have NOT experienced the elevated fault rate, verifying they lack the identified common factor.
Test Points
Fault rate trend vs. historical baseline
Common factor analysis across affected locations (installation date, batch, contractor, maintenance history)
Representative sample investigation results
Hypothesis testing against unaffected locations
Root Cause Verification

Implement the identified corrective/preventive action across the full at-risk population and monitor the airfield-wide fault rate over an extended subsequent period to confirm it returns to baseline.

Corrective Action
  • Address the specific common cause identified, whether through proactive replacement of an at-risk batch, correction of a maintenance practice, or another targeted intervention across all affected locations rather than one-by-one reactive repair.
Preventive Action
  • Establish and maintain a centralised fault history database with sufficient detail (installation date, batch, contractor) to enable future pattern detection at the earliest possible point.
  • Conduct periodic airfield-wide fault rate trend reviews rather than only investigating fault clusters after they become obvious.
  • Treat any statistically significant fault rate increase as a trigger for RCA rather than continuing purely reactive repair.
Related References

SOP: SOP-FCS-20 (Airfield-Wide Root Cause Analysis Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, general RCA methodology (5-Why, fishbone/Ishikawa)

Diagram: Airfield-wide fault location and trend map

Case Study Cross-Reference: Division 24 — Complete Runway Lighting Failure; Division 13 — Repeated Cable Fault (CBL-369)

Rev 0 — Initial issue
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Frequently Asked Questions

Quick answers about Division 25 — Field Case Study Troubleshooting in the AGL Troubleshooting Atlas.

Q1What does Division 25 of the AGL Troubleshooting Atlas cover?

Division 25 is the Field Case Study Troubleshooting reference. It publishes 20 diagnostic topics, FCS-581 to FCS-600, 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 25?

The 20 topics are FCS-581 to FCS-600: CCR Trip After Rain; CCR Trip at Maximum Intensity; One Light Failure in Healthy Circuit; Multiple Lights Failure After Cable Work; Transformer Failure After Flooding; Transformer Overheating Under Load; Connector Burning in Series Circuit; Cable Insulation Failure Underground; Intermittent Earth Fault; Repeated LED Fixture Failure; Sign Board Partial Illumination; PAPI Incorrect Indication; Approach Light Photometry Failure; Runway Edge Light Alignment Failure; Taxiway Light Water Ingress; Stop Bar Control Failure; ALCMS Communication Failure; Remote CCR Control Failure; Photometry Measurement Discrepancy; Recurring Airport AGL Failure RCA.

Q4How does a diagnostic procedure begin in Division 25?

Each procedure starts with observation before any intervention. For example, FCS-581 (CCR Trip After Rain) begins: Correlate the CCR trip log precisely against rainfall timing and intensity from the site weather station over several events.

Q5What safety precautions apply in Division 25?

Each topic lists its own precautions. For example, FCS-581 (CCR Trip After Rain) starts with: LOTO before all cable/joint work.

Q6Which SOPs are referenced in Division 25?

Related references in the topics include SOP-FCS-01 (Field Case Investigation Procedure), SOP-FCS-02 (Field Case Investigation Procedure), SOP-FCS-03 (Field Case Investigation Procedure), SOP-FCS-04 (Field Case Investigation Procedure), SOP-FCS-05 (Field Case Investigation Procedure), SOP-FCS-06 (Field Case Investigation Procedure), SOP-FCS-07 (Field Case Investigation Procedure) and SOP-FCS-08 (Field Case Investigation Procedure), and 12 more.

Q7Which standards are referenced in Division 25?

Where a standard applies, it appears in the topic's Related References. Those cited in this division include IEC 60364, FAA AC 150/5340-30, IEC 60502, FAA AC 150/5345-46, ICAO Annex 14 Vol I, IEC 60076, FAA AC 150/5345-47, FAA AC 150/5345-26, IEC 62031 and FAA AC 150/5345-44, among others.

Q8How can I find a specific topic in Division 25 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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