Blackwell Reference Online

Extract

There are three main ways of measuring failure: failure rates (how often a failure occurs), reliability (the chances of a failure occurring), and availability (the amount of available useful operating time). “Failure rate” and “reliability” are different ways of measuring the same thing, i.e., the propensity of an operation, or part of an operation, to fail. Availability, on the other hand, is one measure of the consequences of failure in the operation. Failure rate (FR) is calculated as the number of failures over a period of time, e.g., the number of security breaches per year at an airport, or the number of failures over a defined operating time for an aircraft engine. FR is usually calculated from examining actual operating or test data. It can be measured either as a percentage of the total number of products tested or as the number of failures over time. Failure, for most parts of an operation, is a function of time. At different stages during the life of anything, the probability of it failing will be different. The probability of a piece of equipment failing is relatively high when it is first used. Any small defect in the material from which the equipment was constructed or in the way it was assembled might cause it to fail. If the equipment survives this initial stage it could still fail at any point, but the longer it survives, the more likely its failure becomes. Most ... log in or subscribe to read full text