A cross-system reference of AGL fault-isolation methods — not tied to a single fixture type, but applicable across every division in the Atlas. Covers electrical isolation techniques (current, voltage, insulation resistance, resistance, continuity, clamp, thermal), inspection-based methods (visual, photometry), data-driven methods (event logs, CCR alarms, ALCMS data, maintenance history, failure pattern analysis, comparative measurement), and structural techniques (sectional testing, component substitution, circuit segmentation, environmental reproduction, and root cause confirmation). Each topic follows the full engineering diagnostic record: application → system/method scope → diagnostic indicators → procedure → test points → confirmation → follow-up action → best practice.
Application — Used whenever a series circuit (constant-current loop) shows abnormal behaviour — a dark fixture, dim run, tripped CCR, or unexpected current reading — to localise the fault to a circuit segment or component before physical excavation or fixture removal.
Series (constant-current) AGL circuits fed by a CCR, including runway/taxiway edge, centreline, and approach light loops.
After repair, re-measure current at the CCR and at the previously bracketed segment and confirm it matches the commanded setpoint within tolerance across all steps.
Always record baseline current readings at commissioning and during routine PM visits so a future fault can be diagnosed against a known-good reference; test current at multiple intensity steps, not just one, since some faults only manifest under load.
SOP: SOP-ADT-01 (Series Circuit Current Fault Isolation Procedure), SOP-CCR-04 (CCR LOTO Procedure)
Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30
Diagram: Series Circuit Current Loop Reference
Case Study: Division 01 — CCR Troubleshooting
Application — Used to localise faults in parallel or low-voltage circuits, or to check voltage drop across specific components (transformers, connectors, cable runs) within a series circuit, where a current reading alone does not pinpoint the exact fault location.
Parallel AGL circuits (e.g., obstruction lights, some sign circuits) and voltage-drop testing across components within series circuits.
After repair, re-measure voltage at all previously tested points and confirm values match the expected design voltages within tolerance.
Maintain an up-to-date voltage reference table for each circuit at commissioning so future voltage-drop testing has a valid baseline for comparison; test at multiple points systematically rather than jumping straight to the suspected fixture.
SOP: SOP-ADT-02 (Voltage Drop Fault Isolation Procedure)
Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, IEC 60364
Diagram: Circuit Voltage Reference Table
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used to detect and localise insulation breakdown in cables, transformers, and fixture wiring — the primary method for identifying cable faults, water ingress, and winding failures before they cause a circuit-level outage.
Primary series cable, isolation transformers, and fixture internal wiring across all AGL circuit types.
After repair, megger the full affected loop end-to-end and confirm it meets or exceeds the minimum acceptable insulation resistance before re-energising.
Include full-loop insulation resistance testing in the periodic PM programme and trend the results year over year per segment to catch degrading insulation before it causes an outage.
SOP: SOP-ADT-03 (Insulation Resistance Test Procedure), SOP-RCL-02 (Series Circuit Fault Location Procedure)
Standards: IEC 60364, ICAO Annex 14 Vol I, FAA AC 150/5340-30
Diagram: Cable Route and Joint Location Drawing
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used to measure the DC resistance of conductors, connections, and components directly, distinct from insulation testing, to identify high-resistance joints, corroded connectors, or an out-of-spec winding/loop resistance.
Cable conductors, connectors, splices, and low-voltage component windings across AGL circuits.
After repair, re-measure resistance at the corrected point and confirm it now matches the expected/reference value.
Maintain a reference table of expected resistance values by cable type/length and component model to speed future comparisons; treat a trending increase in resistance as an early warning rather than waiting for outright failure.
SOP: SOP-ADT-04 (Resistance Measurement Fault Isolation Procedure)
Standards: IEC 60364, ICAO Annex 14 Vol I
Diagram: Conductor Resistance Reference Table
Case Study: Division 25 — Field Case Study Troubleshooting
Application — Used to quickly confirm whether a conductor, fuse, connector, or simple component provides an unbroken electrical path, typically as a fast first check before more detailed resistance or insulation testing.
Fuses, control wiring, low-voltage signal/interlock circuits, and short conductor runs across AGL and CCR systems.
After repair or replacement, re-run the continuity check and confirm a stable, expected result.
Use continuity testing as a fast first-pass check before more time-consuming resistance or insulation testing, especially for control and interlock circuits.
SOP: SOP-ADT-05 (Continuity Test Procedure)
Standards: IEC 60364, ICAO Annex 14 Vol I
Diagram: CCR/Control Wiring Diagram
Case Study: Division 01 — CCR Troubleshooting
Application — Used to measure current non-invasively at multiple points without breaking the circuit, particularly useful for quick comparative checks across parallel branches or for locating an unexpected current path.
Any accessible conductor carrying AC or DC current where a clamp meter can be applied without disconnection — series loops, parallel branch circuits, ground conductors.
After repair, re-clamp all previously tested points and confirm current is balanced across branches and zero on the ground conductor as expected.
Keep a clamp meter with min/max/inrush capture as a standard first-response tool for AGL field diagnostics, since it allows rapid non-invasive comparison across multiple points without circuit interruption.
SOP: SOP-ADT-06 (Clamp Current Survey Procedure)
Standards: ICAO Annex 14 Vol I, IEC 60364
Diagram: Circuit Layout with Parallel Branch/Ground Reference
Case Study: Division 01 — CCR Troubleshooting
Application — Used to detect abnormal heating in connectors, terminations, transformers, and CCR components, often revealing a developing high-resistance or overload fault before it causes an outright failure.
CCR terminals and busbars, transformer connections, in-pavement base-can connectors, and any accessible electrical termination point.
After correcting the identified termination or component, re-scan under load and confirm the temperature differential has resolved to within normal range.
Include periodic thermal imaging of CCR terminals and major connections in the PM programme, particularly before peak seasonal loading, to catch developing connection issues before they cause a failure.
SOP: SOP-ADT-07 (Thermal Inspection Procedure), SOP-CCR-04
Standards: NFPA 70B (Electrical Equipment Maintenance, where adopted), ICAO Annex 14 Vol I
Diagram: CCR Panel Thermal Reference Points
Case Study: Division 01 — CCR Troubleshooting
Application — Used as the first-pass, no-instrument diagnostic step for any reported AGL fault, often revealing an obvious cause (damage, contamination, missing component) without the need for electrical testing.
All AGL fixtures, base cans, cable runs, and CCR/control equipment accessible for direct visual examination.
After correcting a visually-identified fault, re-inspect and, where applicable, re-test electrically to confirm the fixture or circuit now performs correctly.
Always perform and document a thorough visual inspection before instrumented testing — it is fast, low-risk, and frequently identifies the cause directly, and its findings also inform which instrumented test to run next.
SOP: SOP-ADT-08 (Visual Inspection Procedure)
Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30
Diagram: Base-Can/Fixture Inspection Checklist
Case Study: Division 25 — Field Case Study Troubleshooting
Application — Used when a fixture appears electrically and visually normal but is suspected of an optical or output-quality fault, or as part of scheduled acceptance/compliance testing, drawing on the full set of photometric diagnostic topics (Division 18).
Any AGL fixture requiring photometric verification of intensity, alignment, spread, distribution, or chromaticity.
Once the identified photometric fault is corrected per its Division 18 procedure, re-run the full photometric test and confirm all parameters pass.
Use photometry as a targeted follow-up test once electrical and visual causes have been ruled out, rather than as the first response to every reported issue, to make efficient use of test time and equipment.
SOP: SOP-ADT-09 (Photometric Fault Isolation Procedure); cross-reference Division 18 — AGL Photometry Troubleshooting (PHM-451 through PHM-470)
Standards: ICAO Annex 14 Vol I Attachment A, FAA AC 150/5340-30
Diagram: Isocandela and Colour Box Reference Set
Case Study: Division 18 — AGL Photometry Troubleshooting
Application — Used to reconstruct the sequence and timing of a fault from the CCR/ALCMS event/alarm log, particularly valuable for intermittent faults, faults reported after the fact, or faults that self-cleared before a technician arrived.
CCR and ALCMS event/alarm logging systems and their historical data records.
After the physical fault is corrected, monitor the event log over the following period and confirm the previously recurring alarm pattern does not reappear.
Review event logs as a standard first step for any reported intermittent or previously self-cleared fault, since the pattern often narrows the search dramatically before any equipment is touched.
SOP: SOP-ADT-10 (Event Log Review Procedure)
Standards: ICAO Annex 14 Vol I
Diagram: CCR/ALCMS Event Log Export Template
Case Study: Division 01 — CCR Troubleshooting
Application — Used to interpret specific CCR alarm codes and indications directly as the starting point for fault isolation, since the alarm type itself often indicates the fault category (overcurrent, undercurrent, open circuit, ground fault, etc.).
CCR alarm/annunciation system and its defined alarm code set.
After the underlying field or CCR fault is corrected, confirm the alarm clears and does not recur under normal and test-step operation.
Keep the CCR alarm code reference readily available to field technicians so alarm type can immediately direct the correct fault-isolation method rather than defaulting to a generic full-circuit search.
SOP: SOP-ADT-11 (CCR Alarm Response Procedure), SOP-CCR-01
Standards: ICAO Annex 14 Vol I, FAA AC 150/5345-10 (Constant Current Regulators)
Diagram: CCR Alarm Code Reference Table
Case Study: Division 01 — CCR Troubleshooting
Application — Used to leverage the broader Airfield Lighting Control and Monitoring System’s data set — individual fixture status, historical trending, and system-wide views — beyond a single CCR’s alarm output, particularly for faults spanning multiple circuits or requiring historical trend analysis.
ALCMS central monitoring system and its fixture-level and circuit-level data records across the airfield.
After the underlying fault is corrected, confirm ALCMS reports normal status for the affected fixture(s)/circuit(s) and that historical trending shows the parameter has stabilised.
Review ALCMS trend data periodically as part of the PM programme, not only when a fault is reported, to catch gradually degrading fixtures or circuits before they cause an operational outage.
SOP: SOP-ADT-12 (ALCMS Data Review Procedure)
Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30
Diagram: ALCMS System Architecture and Data Path Drawing
Case Study: Division 01 — CCR Troubleshooting
Application — Used to review a fixture’s, circuit’s, or component’s prior maintenance and repair records to identify recurring issues, recently replaced parts, or a documented pattern that shortens the current diagnostic effort.
Fixture/circuit/component maintenance and repair history records across the AGL asset base.
After applying a more thorough corrective action informed by the history review, monitor the asset through the next one to two maintenance cycles and confirm the fault does not recur.
Make maintenance history review a standard first step for any fault at a location with prior recorded issues, and ensure every repair is logged with enough detail (part numbers, root cause, corrective action) to be useful for this purpose in the future.
SOP: SOP-ADT-13 (Maintenance History Review Procedure); cross-reference PHM-468 (Repeated Photometry Failure)
Standards: ICAO Annex 14 Vol I
Diagram: Asset Maintenance History Log Template
Case Study: Division 25 — Field Case Study Troubleshooting
Application — Used to step back from a single fault event and analyse failure data across multiple fixtures, circuits, or time periods to identify systemic trends — a specific fixture model failing early, a specific circuit section failing repeatedly, or a seasonal pattern — that individual fault reports do not reveal on their own.
Airfield-wide or system-wide fault and maintenance data across multiple assets and time periods.
After a systemic corrective programme is implemented (batch replacement, drainage improvement, design change), monitor failure rates for the affected population over subsequent cycles and confirm the rate has returned to normal.
Periodically run failure pattern analysis across the full asset base as part of the PM programme, not only in response to an unusually high number of individual complaints, to catch systemic issues early.
SOP: SOP-ADT-14 (Failure Pattern Analysis Procedure), SOP-PHM-14 (Chronic Fault Escalation Procedure)
Standards: ICAO Annex 14 Vol I
Diagram: Fleet-Wide Failure Rate Reporting Template
Case Study: Division 25 — Field Case Study Troubleshooting
Application — Used to diagnose a suspect fixture, circuit, or component by directly comparing its measured values against a known-good equivalent operating under the same conditions, particularly useful when an absolute specification is unavailable, ambiguous, or when instrument calibration itself is in question.
Any fixture, circuit segment, or component with a directly comparable equivalent elsewhere on the same or a similar system.
After replacing or repairing the confirmed faulty unit, re-compare it against the known-good reference and confirm the values now align within normal variation.
Use comparative measurement particularly when absolute pass/fail criteria are unclear or when instrument calibration itself is in doubt, since a side-by-side comparison under identical conditions removes much of that ambiguity.
SOP: SOP-ADT-15 (Comparative Measurement Procedure)
Standards: ICAO Annex 14 Vol I
Diagram: Comparative Test Setup Reference
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used to systematically divide a long circuit, cable run, or system into sections and test each in turn, bracketing the fault into a progressively smaller segment — the standard approach when a fault’s general presence is known but its exact location along an extended run is not.
Long series/primary cable loops, extended parallel circuit runs, and multi-segment systems where the fault location along the run is not yet known.
After repairing the identified section, re-test the full run end-to-end and confirm it now passes consistently across all previously tested points.
Favor a bisection (midpoint-first) approach over sequential end-to-end testing where the run has many accessible test points, since it locates the fault in far fewer test operations on a long run.
SOP: SOP-ADT-16 (Sectional/Bisection Test Procedure), SOP-RCL-02
Standards: ICAO Annex 14 Vol I
Diagram: Circuit Route Drawing with Test Point Map
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used to confirm a suspected faulty component by temporarily substituting a known-good unit of the same type and observing whether the fault clears — particularly effective for components that are difficult to test in place but easy to swap (modules, transformers, relays, cards).
Field-replaceable AGL and CCR components — lamp/LED modules, isolation transformers, control relays/cards, and similar plug-in or bolt-in parts.
After permanently replacing the confirmed-faulty component, re-verify full correct operation and, where applicable, confirm photometric or electrical parameters meet specification.
Keep a small stock of verified known-good substitute components for common field-replaceable parts specifically for diagnostic swap-testing, separate from general spares stock, to keep this method fast and reliable.
SOP: SOP-ADT-17 (Component Substitution Test Procedure)
Standards: ICAO Annex 14 Vol I
Diagram: Field-Replaceable Component Reference List
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used to deliberately open and isolate specific circuit segments (via existing isolators, splices, or by temporarily disconnecting sections) to determine whether a fault lies within a given segment or is only present when segments are connected together — distinct from sectional testing in that it actively reconfigures the circuit rather than only measuring at fixed points.
Circuits with defined sectionalising points (isolators, splice kits, removable links) allowing controlled segment-by-segment isolation.
After repairing the identified segment, reconnect all segments, re-energise, and confirm the full circuit operates correctly under all normal operating conditions.
Where a circuit is being newly designed or upgraded, include permanent, clearly identified sectionalising points at logical intervals specifically to support this fault-isolation method in the future.
SOP: SOP-ADT-18 (Circuit Segmentation Test Procedure), SOP-RCL-02
Standards: ICAO Annex 14 Vol I
Diagram: Circuit Layout with Segment Boundary Map
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used for intermittent faults that only occur under specific environmental conditions (rain, temperature extremes, vibration from aircraft/vehicle movement) that are not present at the time of a routine inspection, by deliberately reproducing or waiting for the relevant condition to observe the fault directly.
Any AGL circuit or fixture with a reported intermittent fault correlated with a specific environmental or operational condition.
After correcting the identified fault, repeat the environmental reproduction test and confirm the fault no longer occurs under the same condition that previously triggered it.
Reserve environmental reproduction testing for faults where event log correlation or field reports already point to a specific condition, since it is more time-and-resource-intensive than other fault-isolation methods and works best when targeted rather than exploratory.
SOP: SOP-ADT-19 (Environmental Reproduction Test Procedure); cross-reference ADT-610 (Fault Isolation Using Event Logs)
Standards: ICAO Annex 14 Vol I
Diagram: Environmental Test Condition Reference
Case Study: Division 05 — Runway Centreline Light Troubleshooting
Application — Used as the final, closing step of any fault-isolation effort — regardless of which method(s) identified the likely fault — to positively confirm the true underlying root cause before closing out the work order, ensuring a symptom was not mistaken for the cause and preventing premature closure that leads to repeat failures.
Any AGL fault investigation, applied as the concluding step after any of the other Division 26 fault-isolation methods.
Full restoration of normal operation across all relevant tests, ideally repeated across more than one operating condition or over a short monitoring period, constitutes the confirmation itself.
Never close a fault investigation on the basis of a single "it works now" check alone; always re-test under representative conditions and, where practical, positively confirm the physical failure mechanism of the removed/repaired component, since this is what makes future pattern analysis and repeat-failure detection possible.
SOP: SOP-ADT-20 (Root Cause Confirmation and Closure Procedure); cross-reference ADT-614 (Fault Isolation Using Failure Pattern Analysis), PHM-468 (Repeated Photometry Failure)
Standards: ICAO Annex 14 Vol I
Diagram: Fault Investigation Closure Checklist
Case Study: Division 25 — Field Case Study Troubleshooting
Quick answers about Division 26 — Advanced Diagnostic Topics in the AGL Troubleshooting Atlas.
Division 26 is the Advanced Diagnostic Topics reference. It publishes 20 diagnostic topics, ADT-601 to ADT-620, in a single subsection.
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).
The 20 topics are ADT-601 to ADT-620: Fault Isolation Using Circuit Current; Fault Isolation Using Circuit Voltage; Fault Isolation Using Insulation Resistance; Fault Isolation Using Resistance Measurement; Fault Isolation Using Continuity Testing; Fault Isolation Using Clamp Measurement; Fault Isolation Using Thermal Inspection; Fault Isolation Using Visual Inspection; Fault Isolation Using Photometry; Fault Isolation Using Event Logs; Fault Isolation Using CCR Alarms; Fault Isolation Using ALCMS Data; Fault Isolation Using Maintenance History; Fault Isolation Using Failure Pattern Analysis; Fault Isolation Using Comparative Measurements; Fault Isolation by Sectional Testing; Fault Isolation by Component Substitution; Fault Isolation by Circuit Segmentation; Fault Isolation by Environmental Reproduction; Fault Isolation by Root Cause Confirmation.
Each procedure starts with observation before any intervention. For example, ADT-601 (Fault Isolation Using Circuit Current) begins: Record the CCR’s commanded current step and compare to the actual output current shown on the CCR/ALCMS display.
Each topic lists its own precautions. For example, ADT-601 (Fault Isolation Using Circuit Current) starts with: LOTO before opening any base can or joint for current-loop testing beyond clamp measurement at the CCR.
Related references in the topics include SOP-ADT-01 (Series Circuit Current Fault Isolation Procedure), SOP-CCR-04 (CCR LOTO Procedure), SOP-ADT-02 (Voltage Drop Fault Isolation Procedure), SOP-ADT-03 (Insulation Resistance Test Procedure), SOP-RCL-02 (Series Circuit Fault Location Procedure), SOP-ADT-04 (Resistance Measurement Fault Isolation Procedure), SOP-ADT-05 (Continuity Test Procedure) and SOP-ADT-06 (Clamp Current Survey Procedure), and 15 more.
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, IEC 60364, NFPA 70B, ICAO Annex 14 Vol I Attachment A and FAA AC 150/5345-10.
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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