Mission Reliability. Mission reliability is the probability the system will perform Mission Essential Functions (MEFs) for a period of time under the conditions stated in the mission profile. Mission reliability can also be stated as the probability a system can complete its required operational mission without an OMF. An OMF is a failure that prevents the system from performing one or more MEFs. Two measures of mission reliability are mean time between operational mission failure and item reliability. Mean Time Between Operational Mission Failure (MTBOMF). MTBOMF is the average amount of operating time between OMFs. Alternatively, time can be replaced with cycles, rounds, miles, etc. (i.e., MCBOMF, MRBOMF, MMBOMF, etc.), as appropriate for the system under test. Where: MTBOMF = OT #OMFs OT is Operating Time; the time during a mission profile when the system is turned on and actively performing at least one, if not all, of its functions. # OMFs is the number of Operational Mission Failures. Item Reliability (R). Item reliability is the probability that an item will perform its intended function for a specified interval under stated conditions. Generally this is the probability that an item will perform its MEFs for its specified Mission Duration (MD) under conditions corresponding to its mission profile as stated in the XXX or OMS/MP. MD is the length of a mission as defined in the mission profile. All OMFs, regardless of chargeability, are used in the calculations. Depending upon the nature of the item, either a discrete or continuous reliability model will be used. Generally, the distribution of failure can be assumed to be binomial for discrete items, and exponential for continuous items. Other failure distributions may be used when appropriate. Discrete Model.
Mission Reliability. The probability that a system will perform its required mission critical functions for the duration of a specified mission under conditions stated in the mission profile. [Defense Acquisition University Glossary.] Mission reliability can also be stated as the probability a system can complete its required operational mission without an operational mission failure (OMF). An OMF is a failure that prevents the system from performing one or more mission essential functions. For some systems, mission reliability may be better expressed as a function of Mean Time (miles, rounds, etc.) Between Operational Mission Failure (MTBOMF). (See paragraph 8 for definition.)
