Reliability centered maintenance is a method for deciding what maintenance is worth doing, and it starts from an unusual place: not the machine, but the function the machine performs and the ways that function can be lost. That shift is the whole idea, and it is why RCM often ends up removing tasks from a plan rather than adding them.
The questions RCM actually asks
For each asset the method works through what it is supposed to do, in what ways it can fail to do that, what causes each of those failures, what happens when each occurs, and only then what task would be worth doing about it. The order matters. Starting from the machine produces a list of things you could inspect; starting from the failure and its consequence produces a list of things worth inspecting, which is usually much shorter and better argued.
Why it often shortens the plan
Plans assembled from manufacturer recommendations tend to accumulate tasks that address failure modes which either do not occur at this site or do not matter when they do. Working through consequences exposes those, and reliability based maintenance frequently ends with fewer scheduled tasks and better-targeted ones. That is a genuinely uncomfortable result to present, because a shorter plan looks like less diligence until you can point at the failure modes each remaining task addresses.
What it costs to do properly, and the light version
A full analysis is slow: it wants people who know the equipment in a room together, working asset by asset, and that time is the real reason reliability maintenance programmes stall. The pragmatic version applies the same questions only to the assets whose failure actually hurts, accepts rougher answers, and writes down the reasoning so the next person can argue with it. That is worth far more than a complete analysis that never gets finished.
Questions people ask about reliability centered maintenance
What is reliability centered maintenance in one sentence?
A method that decides maintenance tasks from what an asset does, how that function can be lost, and what each loss costs, rather than from the machine or the manufacturer's default list.
Is reliability centred maintenance different from RCM?
No, it is the same thing with British spelling. Reliability based maintenance and reliability maintenance are used loosely for the same family of ideas.
Does RCM add work to the plan?
Usually it removes some. Plans built from manufacturer defaults carry tasks addressing failure modes that do not occur or do not matter here, and working through consequences exposes them.