Definition
Mean Time to Failure (MTTF) is the average operating time before failure for non-repairable items: components or products that are replaced, not repaired, once they fail. It differs from MTBF specifically in applying to items with a single, terminal failure event rather than repairable systems that return to service after each failure.
Key facts
- Applies specifically to non-repairable items, once it fails, the item is replaced, not repaired and returned to service.
- Distinct from MTBF, which measures average time between failures for repairable systems that continue operating after each repair.
- Calculated as total operating time across a population of items divided by the number of failures observed.
- Commonly used for components like bulbs, sensors, or single-use parts rather than entire repairable machines.
How is Mean Time to Failure calculated?
MTTF measures the average time a non-repairable item operates before it fails for good, calculated by observing a population of identical items, summing their total operating time, and dividing by the number that failed, giving an expected lifetime rather than a guaranteed one.
What influences Mean Time to Failure?
MTBF specifically applies to repairable systems: after a failure, the system is repaired and returns to service, and MTBF measures the average time between those successive failures. MTTF applies to non-repairable items with a single, terminal failure event: the item is retired or replaced, not repaired, once it fails.
FAQ
Frequently asked questions
What does the time to failure of an item under consideration describe?
Mean Time to Failure (MTTF): the average operating time before a non-repairable item fails for good, distinct from MTBF, which applies to repairable systems returned to service after each failure.
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