TOOLS

There are many R&M tools. The ones mentioned here are required in the Design and Development Planning (4.4.2) section of the TE Supplement. Many others beyond the few that are addressed here are available and can improve reliability.

Mean Time Between Failure (MTBF) is defined as the average time between failure occurrences. It is simply the sum of the operating time of a machine divided by the total number of failures. For example, if a machine runs for 100 hours and breaks down four times, the MTBF is 100 divided by 4 or 25 hours. As changes are made to the machine or process, we can measure the success by comparing the new MTBF with the old MTBF and quantify the action that has been taken.

Mean Time to Repair (MTTR) is defined as the average time to restore machinery or equipment to its specified conditions. This is accomplished by dividing the total repair time by the number of failures. It is important to note that the MTTR calculation is based on repairing one failure and one failure only. The length of time it takes to repair each failure directly affects up-time, up-time %, and capacity. For example, if a machine runs 100 hours and has eight failures recorded with a total repair time of four hours, the MTTR for this machine would be four hours divided by eight failures or .5 hours. This is the mean time it takes to repair each failure.

Fault Tree Analysis (FTA) is an effect-and-cause diagram. It is a method used to identify the root causes of a failure mode using symbols developed in the defense industry. The FTA is a great prescriptive method for determining the root causes associated with failures and can be used as an alternative to the Ishikawa Fish Bone Diagram. It compliments the Machinery Failure Mode and Effects Analysis (MFMEA) by representing the relationship of each root cause to other failure-mode root causes. Some feel the FTA is better suited than the FMEA to providing an understanding of the layers and relationships of causes. An FTA also aids in establishing a troubleshooting guide for maintenance procedures. It is a top down approach.

Life Cycle Costs (LCC) are the total costs of ownership of the equipment or machinery during its operational life. A purchased system must be supported during its total life cycle. The importance of life cycle costs related to R&M is based on the fact that up to 95% of the total life cycle costs are determined during the early stages of the design and development of the equipment. The first three phases of the equipment's life cycle are typically identified as non-recurring costs. The remaining two phases are associated with the equipment's support costs.