Reliability V. Availability
Reliability: The probability that an item will perform satisfactorily for a given period of time under a stated set of conditions.
Availability: The probability that an item will be capable of performing satisfactorily at some point in the future provided that it is currently performing satisfactorily.
Maintainability: The probability that an item can be returned to full service after a failure in a given period of time under a stated set of conditions.
Availability is a function of reliability and maintainability. The greatest gains in availability are achieved by a two pronged approach that eliminates unnecessary work and makes the necessary work more efficient.
Reliability is a function of how well items are designed, manufactured, installed, operated and maintained. Inherent reliability is set by the design of the item. Each activity after that has a negative impact on reliability. The goal for reliability engineers in the subsequent phases is to develop systems that minimize those negative impacts.
Maintainability is a function of the design and implementation of support systems. The installation needs to be designed to enhance the ability to perform maintenance activities. Support systems such as stores, the CMMS, HR, planning and scheduling, policies and procedures, and training need to be implemented in a way that minimizes the amount of time it takes to perform maintenance activities.
Again a very good article from you Bill. Hope it will be read and used. At least it is very clear and completely accurate.
Let me add a John Egnatz word, "Versability" Eggy himself coined that word. Moving right along you have another John Egnatz word which you will use because you have a bit of "Obviousity", don't you ? Use them well everyone. Oh just one more thing, "your curious nature has motivated you to ask the obvious question". Hasn't it ? There you have it "Obviousity" brought to you by Eggy in Chicago. Eggy has "Versability.
Funny how so many use the two as if they are interchangeable.