PREVENTIVE VS PREDICTIVE
Two maintenance philosophies for AGL systems — preventive maintenance is performed at planned time or usage intervals to reduce the probability of failure, while predictive maintenance uses actual equipment-condition data and trend analysis to determine when maintenance is genuinely needed. Preventive asks "when does the schedule say to service it?" Predictive asks "what does the equipment's condition say?"
At a Glance
| Feature | Preventive Maintenance | Predictive Maintenance |
|---|---|---|
| Basis | Time / operating hours / cycles | Actual equipment condition |
| Main objective | Prevent likely failures | Predict failure before it occurs |
| Trigger | Scheduled interval | Condition/trend reaches a limit |
| Data requirement | Relatively low | Higher |
| Sensors / monitoring | Not always required | Often required |
| Maintenance timing | Fixed or predefined | Condition-dependent |
| Unnecessary maintenance | Possible | Generally reduced |
| Initial cost | Lower | Higher |
| Technical complexity | Lower | Higher |
| AGL example | Replace lamp every defined interval | Replace/inspect based on measured degradation |
Preventive Maintenance
Preventive maintenance asks: "When should we service this equipment according to the maintenance schedule?" The work is performed at a predefined interval, even if the equipment is currently operating normally.
INSTALLATION
│
▼
OPERATING
│
▼
SCHEDULED INTERVAL
│
▼
MAINTENANCE
│
▼
RETURN TO SERVICE
│
▼
NEXT INTERVAL
Example — a 12-month AGL fixture service: clean the optical system, inspect connections, check alignment, and replace specified components on schedule.
Predictive Maintenance
Predictive maintenance asks: "What is the actual condition of this equipment, and when is maintenance likely to become necessary?" Data is collected, trended, and used to plan work before an operational failure occurs.
EQUIPMENT
│
▼
MEASURE CONDITION
│
▼
COLLECT DATA
│
▼
ANALYSE TREND
│
▼
PREDICT DEGRADATION
│
▼
PLAN MAINTENANCE
Example — a CCR trended on output current, temperature, alarm history, operating hours, and component condition, with maintenance planned once the trend analysis flags a concern.
Calendar-Driven vs Deterioration-Driven
TIME
│
├─────────┬─────────┬─────────
│ │
SERVICE SERVICE SERVICE
CONDITION
│
│ /
│ /
│ /
│____/____________ TIME
↑
MAINTENANCE
REQUIRED
Easy memory: Preventive = maintain based on time or usage. Predictive = maintain based on condition and trends.
Simple, Schedulable, Low-Complexity
Preventive maintenance is the practical baseline for most AGL systems because it is simple to plan, easy for maintenance teams to implement, and does not depend on sensors or monitoring infrastructure. The main trade-off is that equipment may be serviced earlier than actually necessary.
- Simple to schedule and budget
- Lower monitoring and data-collection cost
- Easy for maintenance teams to implement consistently
- Lower technical complexity and initial investment
Targeted, Data-Driven, Condition-Aware
Predictive maintenance becomes valuable where CCRs, LED fixtures, control systems, or other critical equipment can provide sufficient condition data to identify degradation before it becomes an operational failure. It generally reduces unnecessary replacement and makes better use of remaining equipment life, at the cost of higher technical complexity.
- Maintenance can be better targeted to actual need
- Reduced unnecessary replacement of serviceable parts
- Better use of equipment life
- Potentially lower unplanned downtime
CCR Cooling Fan
Preventive Approach
EVERY 12 MONTHS
│
▼
INSPECT / SERVICE FAN
It makes no difference whether the fan has logged 2,000, 4,000, or 6,000 operating hours — the maintenance occurs according to the schedule.
Predictive Approach
FAN CONDITION
│
├── Vibration
├── Temperature
├── Current
└── Noise
│
▼
TREND ↑
│
▼
BEARING DEGRADATION
SUSPECTED
│
▼
PLAN REPLACEMENT
Maintenance is performed once the monitored condition indicates that degradation is actually developing.
Runway Light
Preventive Approach
RUNWAY LIGHT
│
▼
SCHEDULED INSPECTION
│
▼
CLEAN LENS
│
▼
CHECK ALIGNMENT
│
▼
CHECK CONNECTIONS
The work is performed at predefined intervals regardless of the fixture's current output.
Predictive Approach
LIGHT OUTPUT
│
100%
↓
98%
↓
95%
↓
92%
↓
TREND ANALYSIS
A declining output trend can flag maintenance before the light reaches an unacceptable condition. Exact acceptance limits must come from the applicable project/maintenance criteria.
Predictive ≠ Preventive
Predictive maintenance is actually a condition-based maintenance approach — a distinct branch from preventive within the broader maintenance hierarchy.
MAINTENANCE
│
├── Corrective
│ │
│ ▼
│ After failure/defect
│
├── Preventive
│ │
│ ▼
│ Time / usage based
│
└── Predictive
│
▼
Condition / trend based
Key point: all predictive maintenance is proactive, but not all preventive maintenance is predictive.
Equipment-by-Equipment View
| AGL Equipment | Preventive Maintenance | Predictive Maintenance |
|---|---|---|
| Runway light | Scheduled cleaning/inspection | Photometric degradation trend |
| Taxiway light | Scheduled inspection | Output/condition trend |
| CCR | Scheduled servicing | Temperature/current/alarm trends |
| Isolation transformer | Periodic testing | Condition monitoring where available |
| Control panel | Scheduled inspection | Alarm/event trend analysis |
| AGL cable circuit | Periodic electrical testing | Insulation/condition trend where monitored |
| LED fixture | Scheduled inspection | LED output/thermal degradation trend |
Myths vs Facts
Preventive maintenance remains the practical baseline for most AGL equipment. Predictive maintenance is generally layered on top for critical equipment where sufficient condition data is available, not used as a wholesale replacement.
Preventive maintenance is simple, low-cost, and easy to implement consistently. It remains appropriate wherever monitoring infrastructure is not justified or available.
Predictive maintenance can reduce unnecessary replacement and unplanned downtime, but it carries a higher initial investment in sensors, monitoring, and trained personnel for data analysis.
Predictive maintenance becomes valuable specifically where equipment can provide sufficient condition data to identify degradation trends — not as a default requirement across every component.
Full Engineering Parameters
| Parameter | Preventive Maintenance | Predictive Maintenance |
|---|---|---|
| Maintenance trigger | Time/usage | Condition |
| Failure prevention | Yes | Yes |
| Condition monitoring | Optional | Central to approach |
| Data analysis | Limited | Important |
| Fixed interval | Yes | Not necessarily |
| Initial investment | Lower | Higher |
| Technical complexity | Lower | Higher |
| Maintenance efficiency | Good | Potentially better |
| Equipment utilization | May be lower | Potentially higher |
| Unplanned failure risk | Reduced | Can be further reduced |
Choosing the Right Strategy
DOES THE EQUIPMENT PROVIDE
SUFFICIENT CONDITION DATA TO
IDENTIFY DEGRADATION TRENDS?
│
┌──────┴──────┐
│ │
YES NO
│ │
▼ ▼
PREDICTIVE PREVENTIVE
MAINTENANCE MAINTENANCE
MAY BE REMAINS THE
JUSTIFIED PRACTICAL BASELINE
The final selection depends on:
- Criticality of the equipment to safe airport operation
- Availability of sensors/monitoring for that equipment type
- Cost of unnecessary maintenance versus cost of monitoring
- Availability of trained personnel for trend analysis
- Applicable maintenance program and project/contract requirements
Preventive vs Predictive Maintenance
Preventive maintenance is planned maintenance performed at defined time, usage, or operating intervals to reduce the probability of failure.
Predictive maintenance is condition-based maintenance using measurements, monitoring, and trend analysis to identify when maintenance is actually needed. For AGL systems, preventive maintenance is generally the practical baseline, while predictive maintenance becomes valuable where CCRs, LED fixtures, control systems, or other critical equipment provide sufficient condition data to identify degradation before an operational failure occurs.
Predictive maintenance does not eliminate the need for preventive maintenance — most AGL maintenance programs combine both, applying preventive scheduling as the baseline and predictive monitoring where condition data justifies it.
Engineering & Expert Notes
Collect Reliable Data Before Relying on Predictions
DataPredictive methods need trustworthy measurements.
Keep a Basic Preventive Plan as a Safety Net
FallbackDo not drop schedules until predictions are proven.
Set Action Thresholds in Advance
ManagementDefine what triggers work.
Review Results Regularly
ImprovementUpdate the approach with experience.
Frequently Asked Questions
Preventive maintenance is performed at planned time or usage intervals regardless of actual condition, while predictive maintenance uses measured equipment condition and trend analysis to decide when maintenance is needed.
Not necessarily overall. It can reduce unnecessary replacement and unplanned downtime, but it also requires a higher initial investment in sensors, monitoring systems, and trained analysis personnel.
Predictive maintenance is a condition-based maintenance approach — it uses condition and trend data rather than a calendar to determine when maintenance is needed.
Yes. Most practical AGL maintenance programs use preventive maintenance as the baseline schedule and add predictive monitoring for critical equipment where sufficient condition data is available.
Equipment that can provide continuous or periodic condition data — such as CCRs, LED fixtures, and control systems — is best positioned to benefit, since trend analysis depends on having that data.
No. Preventive maintenance reduces the probability of failure but is not condition-aware, so a fault developing between scheduled intervals may not be caught until the next inspection or until it causes an operational issue.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — general maintenance provisions for visual aids and AGL systems.
ICAO Doc 9137, Part 9
Airport Services Manual, Part 9 — Airport Maintenance Practices, including scheduled and condition-based approaches.
FAA AC 150/5340-26
Maintenance of Airport Visual Aid Facilities — reference framework for scheduled inspection and maintenance of AGL equipment.
DGCA / AAI Requirements
For Indian airport projects, also verify applicable DGCA requirements, AAI requirements, airport-specific maintenance manuals and contract specifications.
The exact interval, monitoring scope, and acceptance limits for any AGL maintenance program must come from the governing standard, the airport's approved maintenance manual, and manufacturer recommendations — not from a general comparison.
Compare the Systems. Then Learn How to Engineer Them.
Understanding the difference between AGL systems is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how AGL systems work as part of a complete airport lighting system, not just as individual components or configurations.