Critical Spare
A critical spare is a replacement part whose unavailability could cause unacceptable equipment downtime, safety exposure, quality risk, or business interruption.
What this term means in maintenance
A critical spare is a replacement part whose unavailability could cause unacceptable equipment downtime, safety exposure, quality risk, or business interruption.
What makes a spare part critical
A part may be critical because of:
- Long supplier lead time
- No acceptable substitute
- High asset criticality
- Lack of standby equipment
- Severe production consequence
- Safety or compliance impact
- Low probability but high consequence
- Special storage or manufacturing requirements
Practical example
A custom gearbox may fail infrequently, but replacement lead time is nine months and no standby machine exists. Holding one spare may be justified despite its cost.
Factors to review
A critical-spares assessment may consider:
- Failure probability
- Installed quantity
- Repairability
- Lead time
- Shelf life
- Storage requirements
- Common use across assets
- Emergency sourcing options
- Consequence of stockout
Critical does not always mean high usage
Frequently used consumables may need high stock levels but may not be critical when they are easily sourced. A rarely used custom component may be highly critical.
Common mistake
Classifying parts only by purchase value can leave low-cost but operationally essential items unprotected.
Related concepts
Related maintenance terms
Keep exploring connected CMMS, reliability, and maintenance planning terms.
MRO Inventory
MRO inventory consists of maintenance, repair, and operations materials used to keep assets and facilities operating but not normally sold as finished products.
Reorder Point
A reorder point is the inventory level at which replenishment should be initiated so expected demand can be covered during supplier lead time.
Asset Criticality
Asset criticality is a structured assessment of how strongly an asset failure could affect safety, environment, quality, production, compliance, cost, and recovery.
Critical Spare FAQs
- How is a critical spare identified?
Review asset criticality, stockout consequence, lead time, substitutes, repairability, standby capacity, and failure probability.
- Is every expensive spare a critical spare?
No. Cost alone does not determine criticality.
- Can a rarely used part be critical?
Yes. Rare demand combined with long lead time and severe stockout consequence can make a part highly critical.