In brief
MTTR (mean time to repair) is the average time that elapses between the failure of a plant and the restoration of its functionality.
Contents
What is MTTR?
MTTR is a key maintenance metric and describes how quickly a failed unit is ready for operation again. It is calculated as the sum of all downtime or repair times divided by the number of failures in a period. Together with MTBF, the mean operating time between failures, it determines the technical availability of a plant.
Depending on the definition, MTTR covers only the actual repair time or the entire time from failure to restart, in which case it is often referred to as mean time to restore. This time is made up of fault reporting, travel, diagnosis, waiting for spare parts and personnel, the actual repair, functional testing and restart. For comparisons, it must therefore be clearly defined which elements are included.
In many companies, the largest share is not the repair itself but the waiting time for spare parts. Good stockholding of critical components, unambiguous master data and prepared sources of supply therefore often reduce MTTR more than faster handling.
In practice: maintenance and procurement
Anyone wishing to reduce MTTR should split downtime into diagnosis, waiting time for material and repair, and record these separately. This makes it clear whether more stock, better parts documentation or training will have the greatest effect.
Synonyms and abbreviations: mean time to repair · mean time to restore · average repair time · mean time to recovery
Frequently asked questions
How is MTTR calculated?
MTTR is the sum of all repair or downtime periods in a given period divided by the number of failures. Example: three failures with two, four and six hours of downtime give twelve hours divided by three, i.e. an MTTR of four hours. It is important always to use the same time definition.
What is the difference between MTTR and MTBF?
MTBF describes the mean operating time between two failures and is therefore a measure of reliability. MTTR describes the mean time until a failed plant is running again and is a measure of maintainability and responsiveness. A high MTBF and a low MTTR together result in high availability.
How can MTTR be reduced?
Effective levers are prompt fault reporting, good diagnostic capabilities, documented repair instructions and trained personnel. The availability of critical spare parts is particularly important: if the part and part number are known and the part is in stock or a source of supply has been prepared, the longest time element, waiting for material, often disappears.
What does MTTR stand for?
MTTR is the abbreviation for mean time to repair, i.e. the average repair time. In some contexts it also stands for mean time to restore or mean time to recovery, meaning the entire time until operation is restored. Which reading applies should be explicitly defined in KPI definitions.