AiVibeQuality, Reliability & Maintenance
Inherent Availability (Ai)
Inherent availability is the probability that equipment is operational when needed, considering only design reliability and corrective maintenance time, calculated as MTBF divided by the sum of MTBF and MTTR.
Availability in reliability engineering expresses the share of time an item is able to perform its function. Inherent availability uses only operating time between failures and active corrective repair time: Ai equals MTBF divided by MTBF plus MTTR. For example, an MTBF of 500 hours and an MTTR of five hours give an inherent availability of about 99 per cent. It reflects the equipment's design and maintainability under ideal support conditions.
Other definitions widen the scope. Achieved availability also includes preventive maintenance time. Operational availability includes all downtime in real operation, such as waiting for technicians, spare parts and administrative or logistics delays, and is often expressed as mean time between maintenance divided by the sum of that figure and mean downtime. Defence, aerospace and process industries use these measures to set requirements for suppliers and to evaluate maintenance and support arrangements.
The availability measures answer different questions, so the type used must be stated. Inherent availability is useful for comparing designs, while operational availability reflects what users experience. Reliability availability should not be confused with the availability factor of OEE, which is run time divided by planned production time and includes stops unrelated to failures, such as changeovers. IEC 60050-192 defines availability and related dependability terms.
Key points
- Ai equals MTBF divided by the sum of MTBF and MTTR.
- Considers only corrective repair time under ideal support conditions.
- Achieved and operational availability add preventive and logistics downtime.
- Different from the availability factor used in OEE.
Where AiVibe comes in
AiAmbA AI Factory use cases include predictive maintenance and visual inspection on textile, automotive and electronics lines. AiAmbA IoT normalises industrial signals from protocols such as OPC UA and MQTT, with driver availability confirmed per installation.
Explore AiVibe’s work in Quality, Reliability & Maintenance →
Related terms
- Mean Time Between Failures (MTBF)Quality, Reliability & Maintenance
- Mean Time to Repair (MTTR)Quality, Reliability & Maintenance
- Reliability Block Diagram (RBD)Quality, Reliability & Maintenance
- Overall Equipment Effectiveness (OEE)Industry 4.0 & Manufacturing Operations
- Failure RateQuality, Reliability & Maintenance