OVERVIEW

The measurement of how good a system or component has performed operationally is often achieved by analyzing the number of events, such as operating time or miles traveled, experienced between failures. The number of miles driven provides an indication of the amount of wear incurred during the life of an automobile. Ships, airplanes, and stationary equipment cannot gauge miles traveled, so they often use operating time as a comparison value. The logistician compares the number of events between failures to the number of failures occurred in order to forecast anticipated support resources.

The most commonly found usage measurement used by the industry and military is Operating Hours. "Mean Time Between (MTB)" will be used throughout this section and others in various example problems. Any other event measurement (such as miles or cycles) may be substituted for Time as required. This unit is sometimes further divided into specific periods of time (for example, Spectrum Flight Hours) to differentiate operation in specific environments or load conditions. Since mean time is an average, single significant digits are sufficient to express these values.

A variety of mean times are used to describe the maintenance frequency of a given item. The definitions and formulas presented in this section are commonly used for major aircraft acquisition programs.

Example:

A commercial airline is analyzing historical maintenance records for their entire fleet of passenger aircraft. Maintenance data is collected in yearly intervals. One group of items being analyzed is the on-board cockpit navigation/communication computers. The collected maintenance...