Question

1. Explain Reliability(R), Maintainability(M) and Availability(A). Discuss how these terms are related to quality. Next provide formulas for reliability, maintainability and availability. Explain how they are calculated based on FAILURE..2. Look for standards related to R, M, and A. Give one example for each term from a standard. Cite the name of the standard.

Answer 1

Reliability, Availability and Maintainability are three system attributes that affect both the utility and the life-cycle costs of a product or system.

Reliability is defined as the probability of a system or system element performing its intended function under stated conditions without failure for a given period of time.

Maintainability is defined as the probability that a system or system element can be repaired in a defined environment within a specified period of time. Increased Maintainability means shorter repair times.

Availability is defined as the probability that a repairable system or system element is operational at a given point in time under a given set of environmental conditions.

RMA interacts with the procurement and quality assurance Organisations with respect to selection and evaluation of materials, components and subsystems.

RMA calculations based on Failure

Reliability can be characterized in terms of the parameters,mean, or any percentile of a reliability distribution. However,in most cases, the exponential distribution is used, and a single value, the mean time to failure (MTTF) for non restorable systems, or mean time between failures (MTBF) for restorable systems are used.

MTTF/MTBF =Top,Tot/nfails

Where Top,Tot I the total operating time and nfails is the number of failures

Maintainability is often characterized in terms of the exponential distribution and the mean time to repair is calculated as

MTTR = Tdown, Tot / noutages

Where Tdown, Tot is the total downtime and noutages is the number of outages

Availability can be calculated from the total operating time and the downtime, or in the alternative, as a function of MTBF and MTTR as

A = Top,Tot / Tdown,Tot + Top, Tot = MTBF / MTBF + MTTR