The decision layer of the handbook. Condition-Based Maintenance uses the actual measured and observed condition of an asset — not its age or a fixed calendar — to determine what maintenance action is justified, when, and how urgently.
The key question: what is the actual condition of the asset, and what maintenance does that condition justify?
Distinction: preventive maintenance runs on a schedule, corrective maintenance responds to failure, and predictive maintenance follows a trend. Condition-Based Maintenance sits apart from all three — it evaluates evidence (physical, environmental, and performance condition) and converts that evidence directly into a classification, a threshold check, and a maintenance decision.
Every condition-based decision in this division follows the same underlying sequence — evidence is collected, the asset is classified, and only then is a maintenance action decided.
Principle: asset age alone should not determine maintenance. Asset condition should.
A generic five-class condition scale — the exact thresholds should be defined in the airport's approved asset-condition matrix.
| Condition | Meaning | Typical Action |
|---|---|---|
| C1 — Good | Normal condition | Routine PM |
| C2 — Satisfactory | Minor deterioration | Monitor |
| C3 — Deteriorating | Significant deterioration | Planned maintenance |
| C4 — Poor | High deterioration / risk | Priority corrective action |
| C5 — Critical | Unacceptable condition | Immediate action / replacement |
AGL Asset Condition Index (ACI): physical condition (25%) + electrical condition (25%) + optical/performance condition (20%) + environmental condition (15%) + reliability/maintenance history (15%) can be combined into a weighted score for airport-wide asset ranking. These bands are a proposed management framework, not universal regulatory acceptance limits — final thresholds should be set against the airport's approved standards and historical data.
Condition combined with trend and risk is far more powerful than condition alone.
| Condition | Trend | Risk | Decision |
|---|---|---|---|
| C1 — Good | Stable | Low | Routine PM |
| C2 — Satisfactory | Stable | Low | Monitor |
| C3 — Deteriorating | Deteriorating | Medium | Increase monitoring |
| C4 — Poor | Stable | Medium | Planned maintenance |
| C4 — Poor | Deteriorating | High | Corrective action |
| C5 — Critical | Any | Very high | Immediate intervention |
Grouped by condition category — click any topic to expand what is assessed and how the condition drives the decision.
Classification: C1 Good → C2 Satisfactory → C3 Deteriorating → C4 Poor → C5 Critical. Exact thresholds are defined in the airport's approved asset-condition matrix.
CBM decision: minor surface deterioration may require monitoring; structural deterioration escalates through repair → replacement → immediate corrective action.
Key question: does the deterioration affect the required optical performance? If yes, corrective maintenance should be initiated.
Classify: Surface → Moderate → Advanced → Structural. Corrosion should also be trended where recurring.
Assess wear as: Normal / Developing / Significant / Operationally unacceptable.
Evidence: cable condition should be evaluated using both physical and electrical evidence.
Risk weighting: a connector with repeated failures should receive a higher condition risk even if it currently functions.
Condition decision: Healthy → Watch → Deteriorating → High Risk → Replacement / major repair candidate.
Trend: repeated LED or driver failures should influence the overall condition rating.
Not just cleaning: moisture is a condition indicator. Repeated moisture may indicate seal failure, a drainage problem, water ingress, condensation, or an installation defect.
Corrective action should address the source of water ingress, not simply remove accumulated water.
Determine whether contamination affects optical output, cooling, electrical equipment, or equipment life.
Treat as a special condition event — not merely routine PM.
Particular attention: equipment operating near environmental or manufacturer limits.
These areas may justify increased inspection / maintenance frequency.
Objective: determine whether deterioration is affecting required visual performance.
Evaluate against: acceptance criteria + historical trend.
Investigate, don't assume: a thermal anomaly should be investigated rather than automatically interpreted as component failure. Possible causes include loose connection, high resistance, overload, component deterioration, poor contact, or normal operating characteristics.
Early trigger: deteriorating optical performance can become a CBM trigger even before complete fixture failure.
Connects physical condition with actual operational performance.
Roll-up: this scale can be converted into the airport's official AGL Asset Condition Index.
Why it works: more useful than a simple pass/fail system — it provides an early intervention window.
Auto-creates: inspection, monitoring, corrective maintenance, or replacement planning — depending on severity.
The core trade-off behind every condition-based corrective action.
The ten-step sequence that carries every asset from condition data collection to an updated condition record.
Confirm the asset and its location.
Physical, environmental, electrical, and optical evidence.
Check against previous condition assessments.
Assign C1–C5 against the condition matrix.
Combine condition with trend.
Normal, Watch, Maintenance, or Critical zone.
Monitor, plan, correct, or replace.
Execute the decided action.
Confirm post-maintenance condition.
Close the loop on the condition record.
Quick answers about condition-based maintenance, based on the topics in this division.
Condition-based maintenance uses the actual measured and observed condition of an asset, not its age or a fixed calendar, to determine what maintenance action is justified, when, and how urgently. The key question is what the actual condition of the asset is and what maintenance that condition justifies.
Division 04 (Condition-Based Maintenance) contains 28 topics in four groups: Group A Physical Condition (11 topics), Group B Environmental Condition (7 topics), Group C Performance Condition (5 topics) and Group D Maintenance Decision (5 topics).
Preventive maintenance runs on time or schedule, corrective maintenance responds to a defect or failure, and predictive maintenance follows a trend. Condition-based maintenance evaluates evidence of physical, environmental and performance condition and converts it directly into a classification, a threshold check and a maintenance decision.
No. The page contrasts a 10-year-old asset that is clean, electrically stable and optically sound, which continues in operation with routine PM, with a 4-year-old asset showing significant corrosion, repeated moisture ingress and increasing connector failures, which justifies condition-based corrective action despite its young age. Asset condition, not age, should determine maintenance.
C1 Good (normal condition, routine PM), C2 Satisfactory (minor deterioration, monitor), C3 Deteriorating (significant deterioration, planned maintenance), C4 Poor (high deterioration or risk, priority corrective action) and C5 Critical (unacceptable condition, immediate action or replacement). Exact thresholds should be defined in the airport's approved asset-condition matrix.
The decision matrix pairs each class with its trend and risk. C1 stable and low risk gets routine PM; C2 stable gets monitoring; C3 deteriorating at medium risk gets increased monitoring; C4 stable at medium risk gets planned maintenance; C4 deteriorating at high risk gets corrective action; and C5 at very high risk gets immediate intervention.
It is a weighted score for airport-wide asset ranking: physical condition 25%, electrical condition 25%, optical/performance condition 20%, environmental condition 15% and reliability/maintenance history 15%. The bands are a proposed management framework, not universal regulatory acceptance limits, so final thresholds should be set against the airport's approved standards and historical data.
Repair applies when the asset remains structurally sound, repair is technically feasible, performance can be restored, repair cost is reasonable and spare parts are available. Replace when structural integrity is compromised, failure is recurring, repair is no longer economical, spares are obsolete or unavailable, performance cannot be reliably restored, or remaining useful life is low or safety and operational risk is high.
Ten steps: identify the asset, collect data, compare history, classify condition, determine risk, check the threshold zone (Normal, Watch, Maintenance or Critical), decide, perform maintenance, verify, and update the record.
Condition-based maintenance is more than logging readings against a threshold.
Build the technical knowledge to interpret condition data, judge when a parameter signals genuine deterioration, and decide the right maintenance response.
Read the condition. Understand the trend. Respond with confidence.
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