Mean Time to Repair (MTTR)

Mean Time to Repair (MTTR) is the average — across all failure events — of the time between detection of a failure and completion of the repair that brings a repairable asset back to production-ready condition. Computation is straightforward: MTTR = (total repair time) / (number of failures). Components: detection time, diagnosis, spare-part supply, the physical repair, testing, and re-commissioning. In SMB practice, spare-parts inventory and operator skill dominate MTTR; a machine that fails at noon and waits for a spare arriving via overnight cargo can push MTTR from 4 hours to 18. MTTR is one of the two main metrics of system reliability; the other is MTBF (mean time between failures). Together they determine equipment availability: Availability = MTBF / (MTBF + MTTR). This equation underlies the Availability component of OEE (Nakajima 1988). Ways to reduce MTTR: stock critical spares, classify recurrent failures via root-cause analysis, train operators in First-Level Maintenance (autonomous maintenance), run maintenance crews on shifts, and design parallel/redundant equipment. MTTR is a core data input to preventive maintenance, equipment replacement, quality control, and job-shop scheduling problems. References: Ebeling 'An Introduction to Reliability and Maintainability Engineering' (1997); Birolini 'Reliability Engineering: Theory and Practice' (2007); Nakajima 'Introduction to TPM' (1988); the IEC 60050-191 standard.