9 Principles of an Effective PM Program based on Reliability Centered Maintenance (RCM)

Written by:
9 Principles of an Effective PM
Program based on Reliability
Centered Maintenance (RCM)
Erik Hupjé
P R E V E N T I V E M A I N T E N A N C E
www.reliabilityacademy.com

Contents
3 Overview
3 Fix it when it breaks
4 Things changed during World War II
4 More maintenance, more failures
6 The birth of Reliability Centered Maintenance
7 Amazing results from the first applications of
Reliability-Centered Maintenance (RCM)
8 The US Department of Defense gets involved in RCM
8 9 Principles from RCM to create an effective PM program
16 RCM FAQs
17 References
18 RCM Infographic

Reliability Academy | 9 Principles of an Effective PM Program based on RCM 3
In this article, I provide a brief history of the development of Reliability Centered Maintenance
(RCM). And from there we explore 9 principles derived from RCM that will help you build an
effective Preventive Maintenance Program. As a maintenance & reliability practitioner, you
should know these RCM principles and live by them.
Overview
Fix it when it breaks
For most of human history, we’ve had a very
simple approach to maintenance: we fixed
things as they broke. This served us well from
our early days huddled around campfires
until about World War II.
In those days industry was not very complex
or highly mechanised. The downtime was not
a major issue and preventing failures wasn’t
a concern.
At the same time, most equipment in use was
simple and more importantly, it was over-de-
signed. This made equipment reliable and
easy to repair. And most plants operated
without any preventive maintenance in place.
Maybe some cleaning, minor servicing, and
lubrication, but that was about it.
This simple ‘fix it when it breaks’ approach
to maintenance is often referred to as First
Generation Maintenance.

4 Reliability Academy | 9 Principles of an Effective PM Program based on RCM
Things changed during
World War II
Wartime increased the demand for many,
diverse products. Yet at the same time,
the supply of industrial labour dropped.
Productivity became a focus. And mechanisa-
tion increased. By the 1950’s more and more
complex machines were in use across almost
all industries. Industry as a whole had come
to depend on machines.
And as this dependence grew, it became
more important to reduce equipment down-
time. ‘Fix it when it’s broken’ no longer suited
industry.
A focus on preventing equipment failures
emerged. And the idea took hold that failures
could be prevented with the right mainte-
nance at the right time. In other words, the
industry moved from breakdown mainte-
nance to time-based preventive maintenance.
Fixed interval overhauls or replacements to
prevent failures became the norm.
This approach to preventive maintenance is
known as Second Generation Maintenance.
More maintenance, more
failures
Between the 1950s and 1970s, the third
generation of maintenance was born in the
aviation industry.
After World War II air travel became widely
accessible. And passenger numbers grew fast.
By 1958 the Federal Aviation Administration
(FAA) had become concerned about reliability.
And passenger safety.

At the time the dominant thinking was that
components had a specific life. That compo-
nents would fail after reaching a certain “age”.
Replacing components before they reached
that age would thus prevent failure. And that
was how you ensured reliability and passen-
ger safety.
In the 1950’s and 1960’s the typical aircraft
engine overhaul was every 8,000 hours. So
when the industry was faced with an increas-
ing number of failures, the conclusion was
easy. Obviously component age must be less
than the 8,000 hours that was being assumed.
So, maintenance was done sooner. The time
between overhauls reduced. Easy, right?
But, increasing the amount of preventive
maintenance had three very unexpected
outcomes. Outcomes that eventually turned
the maintenance world upside down.
First of all, the occurrence of some failures
decreased. That was exactly what everybody
expected to happen. All good.
The second outcome was that a larger number
of failures occurred just as often as before.
That was not expected and slightly confusing.
The third outcome was that most failures
occurred more frequently. In other words,
more maintenance leads to more failures.
That was counter-intuitive. And a shock to
the system.

The birth of Reliability
Centered Maintenance
To say that the results frustrated both the
FAA and the airlines would be an understate-
ment. The FAA worried that reliability had not
improved. And the airlines worried about the
ever-increasing maintenance burden.
So during the 1960’s the airlines and the FAA
established a joint task force to find out what
was going on. After analysing 12 years of data
the task force concluded that overhauls had
little or no effect on overall reliability or safety.
For many years engineers had thought that
all equipment had some form of wear out
pattern. In other words, that as equipment
aged the likelihood of failure increased. But
the study found this universally accepted
concept did not hold true.
Instead, the task force found six patterns
describing the relationship between age and
failure. And that the majority of failures occur
randomly rather than based on age.
The task force findings were used to develop
a series of guidelines for airlines and airplane
manufacturers on the development of reli-
able maintenance schedules for airplanes.
The first guideline titled “Maintenance
Evaluation and Program Development” came
out in 1968. The guide is often referred to
MSG-1 and was specifically written for Boeing
747-100.
The maintenance schedule for the 747-100
was the first to apply Reliability Centered
Maintenance concepts using MSG-1. And it
achieved a 25% to 35% reduction in mainte-
nance costs compared to prior practices.
As a result, the airlines lobbied to remove all
the 747-100 terminology from MSG-1. They
wanted the maintenance schedules for all

new commercial planes designed using the
same process.
The result was MSG-2, released in 1970 titled
“Airline/Manufacturer Maintenance Program
Planning”.
Amazing results from
the first applications
of Reliability-Centered
Maintenance (RCM)
The move to 3rd Generation or Reliability-
Centered Maintenance as outlined MSG-1
and MSG-2 was dramatic.
The DC-8’s maintenance schedule used tradi-
tional, 2nd Generation Maintenance concepts.
It required the overhaul of 339 components
and called for more than 4,000,000 labour
hours before reaching 20,000 operating
hours.
Compare that to the maintenance sched-
ule for the Boeing 747-100, developed using
MSG-1. It required just 66,000 labour hours
before reaching the same 20,000 operating
hours!
Another interesting comparison is to compare
the number of items requiring fixed-time
overhauls. The maintenance for the DC-10
was developed using MSG-2 and required the
overhaul of just 7 items versus the 339 on the
DC-8.
And both the DC-10 and Boeing 747-100 were
larger and more complex than the DC-8.
Impressive results. And the US Department of
Defense (DoD) thought so too.

The US Department of
Defense gets involved in
RCM
So in 1974, the DoD asked United Airlines
to write a report on the processes used to
write reliable maintenance programs for civil-
ian aircraft. And in 1978 Stan Nowlan and
Howard Heap published their report. It was
titled “Reliability Centered Maintenance”.
Since then a lot more work was done to
progress the cause of Reliability-Centered
Maintenance. The airline industry has moved
to MSG-3. John Moubray published his book
RCM2 in the 1990’s introducing Reliability
Centered Maintenance concepts to the indus-
try at large.
Nowadays, RCM maintenance is defined
through international standards. But it’s the
work done in the 60’s and 70’s that culminat-
ed in the Knowlan & Heap report in 1978 that
all modern-day RCM maintenance approach-
es can be traced back to.
That’s now more than 40 years ago. So any
Maintenance & Reliability professional should
be familiar with it by now. It’s been around
long enough. It’s well documented. And wide-
ly available.
Unfortunately, we find that’s not the case. The
principles of modern maintenance as devel-
oped in the journey to Reliability-Centered
Maintenance are not always known or under-
stood. Let alone applied.
The rest of this article will outline those princi-
ples. They should underpin any sound main-
tenance program.
One of the best summaries of these principles
can be found in the NAVSEA RCM Handbook.
I would highly recommend reading it. It is
well written and easy to understand. And the
following Principles of Modern Maintenance
are very much built on the ‘Fundamentals of
Maintenance Engineering’ as described in the
NAVSEA manual.
9 Principles from RCM to
create an effective PM
program
Whether you are developing a new main-
tenance program. Or improving the main-
tenance program for an existing plant. All
reliable maintenance programs should be
based on the following Principles of Modern
Maintenance:
Principle #1: Accept failures
Principle #2: Most failures are
not age-related
Principle #3: Some failure consequences
matter more than others
Principle #4: Parts might wear out, but
your equipment breaks down
Principle #5: Hidden failures must be
found

Principle #6: Identical equipment does
not mean identical maintenance strategy
Principle #7: “You can’t maintain your
way to reliability”
Principle #8: Good maintenance programs
don’t waste your resources
Principle #9: Good maintenance programs
become better maintenance programs
As a Maintenance & Reliability professional,
you must understand these principles.
You must practice them.
You must live by them.
Principle #1: Accept failures
Not all failures can be prevented by mainte-
nance. Some failures are the result of events
outside our control. Think lightning strikes or
flooding. For events like these, more or better
maintenance makes no difference. Instead,
the consequences of events like these should
be mitigated through design.
And maintenance can do little about fail-
ures that are the result of poor design, lousy
construction or bad procurement decisions.
In other cases the impact of the failure is low
so you simply accept a failure (think general
area lighting).
So, good maintenance programs do not try to
prevent all failures. Good maintenance plans
and programs accept some level of failures
and are prepared to deal with the failures
they accept (and deem credible).
Principle #2: Most failure modes
are not age-related
As explained above the RCM research by the
airline industry has shown that 70% – 90% of
failure modes are not age-related. Instead,
for most failure modes the likelihood of
occurrence is random. Later research by the
United States Navy and others found very
similar results.
This research is summarised in the six differ-
ent failure patterns shown in the next page.
Apart from showing that most failure modes
occur randomly. These failure patterns also
highlight that infant mortality is common. And
that it typically persists. That means that the
probability of failure only becomes constant
after a significant amount of time in service.
Don’t interpret Curves D, E, and F to mean
that (some) items never degrade or wear out.
Everything degrades with time, that’s life. But
many items degrade so slowly that wear out
is not a practical concern. These items do not
reach wear out zone in normal operating life.
So what do these patterns tell us about our
reliable maintenance programs?
Historically maintenance was done in the
belief that the likelihood of failure increased
over time (first generation maintenance
thinking). It was thought that well-timed

Figure 6: the failure patterns from various reliability centered maintenance studies

maintenance could reduce the likelihood of
failure. RCM has taught us that for at least
70% of equipment this simply is not the case.
For the 70% of failure modes which has a
constant probability of failure, there is no
point in doing time-based life-renewal tasks
like servicing or replacement.
It makes no sense to spend maintenance
resources to service or replace an item whose
reliability has not degraded. Or whose reliabil-
ity cannot be improved by that maintenance
task.
In practice, this means that 70% – 90% of
equipment failure modes would benefit from
some form of condition monitoring. And
only 10% – 30% can be effectively managed
by time-based replacement or overhaul. Yet
most of our PM programs are full of time-
based replacements and overhauls.
Strictly speaking, the studies that document-
ed the fact that 70% to 90% of failure modes
were random only found this in specific
industries and applications. And they were
not conducted in major industries like oil &
gas, mining, chemical manufacturing, food
processing, power generation etc. So you
could therefore dismiss these results with a
simple “well, we’re in a different industry, so
obviously this doesn’t apply to us”. I strong-
ly believe this principle applies to all heavy
industry (more on that in a future article) and
would strongly encourage you to approach
this with the question “Why wouldn’t it apply
to us?” and then carefully examine what you
could gain from applying this principle.
Principle #3: Some failure
consequences matter more than
others
When deciding on whether to do a mainte-
nance task consider the consequence of not
doing it. What would be the consequence of
letting that specific failure mode occur?
Avoiding that consequence is the benefit of
your maintenance.
The return on your investment.
And that is exactly how maintenance should
be seen: as an investment. You incur a mainte-
nance cost in return for a benefit in sustained
safety and reliability. And as with all good
investments, the benefit should outweigh the
original investment.
So, understanding failure consequences is key
to developing a good maintenance program.
One with a good return on investment.
Just as not all failures have the same prob-
ability, not all failures have the same conse-
quence. Even if it relates to the same type of
equipment.
Consider a leaking tank. The consequence of
a leaking tank is severe if the tank contains a
highly flammable liquid. But if the tank is full
of potable water the consequence might not
be of great concern. Easy, right?
But what if the water is required for fire
fighting?

The same tank, the same failure but now we
might be more concerned. We would not
want to end up in a scenario of not being able
to fight a fire because we had an empty tank
due to a leak.
Apart from the consequence of a failure you
also need to think about the likelihood of the
failure actually occurring.
Maintenance tasks should be developed for
dominant failure modes only. Those failures
that occur frequently and those that have
serious consequences but are less frequent
to rare. Avoid assigning maintenance to
non-credible failure modes. And avoid analys-
ing non-credible failure modes. It eats up your
scarce resources for no return.
A maintenance program should consider
both the consequence and the likelihood
of failures. And since Risk = Likelihood x
Consequence we can conclude that good
maintenance programs are risk-based.
Good maintenance programs use the concept
of risk to assess where to use our scarce
resources to get the greatest benefit. The
biggest return on our investment.
Principle #4: Parts might wear out,
but your equipment breaks down
A ‘part’ is usually a simple component, some-
thing that has relatively few failure modes.
Some examples are the timing belt in a car,
the roller bearing on a drive shaft, the cable
on a crane.
Simple items often provide early signals of
potential failure, if you know where to look.
And so we can often design a task to detect
potential failure early on and take action prior
to failure.
For those simple items which do “wear out”
there will be a strong increase in the proba-
bility of failure past a certain age. If we know
the typical wear outage for a component, we
can schedule a time-based task to replace it
before failure.
When it comes to complex items made
of many “simple” components, things are
different.
All those simple components have their own
failure modes with its own failure pattern.
Because complex items have so many, varied
failure modes, they typically do not exhibit
wear outage. Their failures do not tend to be
a function of age but occur randomly. Their
probability of failure is generally constant as
represented by curves E and F.
Most modern machinery consists of many
componentsandshouldbetreatedascomplex
items. That means no clear wear outage. And
without clear wear out age performing time-
based overhauls is ineffective. And wasteful
of our scarce resources.
Only where we can prove that an item has
wear outage does performing time-based
overhaul or component replacement make
sense.

Principle #5: Hidden failures must
be found
Hidden failures are failures that remain unde-
tected during normal operation. They only
become evident when you need the item
to work (failure on demand). Or when you
conduct a test to reveal the failure – a failure
finding task.
Hidden failures are often associated with
equipment with protective functions.
Something like a high-high pressure trip.
Protective functions like these are not normal-
ly active. They are only required to function by
exception to protect your people from injury
or death. To protect the environment from
a major impact or protect our assets from
major damage. This means we pretty much
always conduct failure finding maintenance
tasks on equipment with protective functions.
To be clear, a failure finding task does not
prevent failure. Instead, a failure finding task
does exactly what its name implies. It seeks
to find a failure. A failure that has already
happened, but has not been revealed to us. It
has remained hidden.
We must find hidden failures and fix them
before the equipment is required to operate.
Principle #6: Identical equipment
does not mean identical
maintenance strategy
Just because two pieces of equipment
are the same doesn’t mean they need the
same maintenance. In fact, they may need
completely different maintenance tasks.
The classic example is two exactly the same
pumps in a duty – standby setup.8 Same
manufacturer, same model. Both pumps
process the exact same fluid under the same
operating conditions. But Pump A is the duty
pump, and Pump B is the standby. Pump A
normally runs and Pump B is only used when
Pump A fails.
When it comes to failure modes Pump B has
an important hidden failure mode: it might
not start on demand. In other words, when
Pump A fails or under maintenance, you
suddenly find that Pump B won’t start. Oops.
Pump B doesn’t normally run so you wouldn’t
know it couldn’t start until you came to start
it. That’s the classic definition of a hidden fail-
ure mode. And hidden failure modes like this
require a failure finding task i.e. you go and
test to see if Pump B will start. But you don’t
need to do this for Pump A because it’s always
running (unless when it’s off or failed).
So when building a maintenance program you
must consider the operating context (RCM
is very clear on this, but other approaches
sometimes neglect operating content).
A difference in criticality can also lead to differ-
ent maintenance needs. Safety or production
critical equipment will need more monitoring
and testing than the same equipment in low
criticality service.
It’s important to reinforce that identical

equipment may need different maintenance
requirements. This is far too often forgotten
or simply ignored for convenience. But you
could find yourself facing critical failures by
ignoring this basic concept. Especially if you
use a library of preventive maintenance tasks.
Principle #7: “You can’t maintain
your way to reliability”
I love this quote from Terrence O’Hanlon
and it’s so very true. Maintenance can only
preserve your equipment’s inherent design
reliability and performance.
If the equipment’s inherent reliability or
performance is poor, doing more mainte-
nance will not help.
No amount of maintenance can raise the
inherent reliability of a design.
To improve poor reliability or performance
that’s due to poor design, you need to change
the design. Simple.
When you encounter failures – defects – that
relate to design issues you need to eliminate
them.
Sure, the more proactive and more efficient
approach is to ensure that the design is right,
to begin with. But all plants startup with design
defects. Even proactive plants. And that’s why
the most reliable plants in the world have an
effective defect elimination program in place.
Principle #8: Good maintenance
programs don’t waste your
resources
This seems obvious, right? But when we
review PM programs we often find main-
tenance tasks that add no value. Tasks that
waste resources and actually reduce reliabili-
ty and availability.
It’s so common for people to say “whilst we
do this, let’s also check this. It only takes 5
minutes.”
But 5 minutes here and there, every week or
every month and we’ve suddenly wasted a lot
of time. And potentially introduced a lot of
defects that can impact equipment reliability
down the line.
Another source of waste in our PM programs
is trying to maintain a level of performance
and functionality that we don’t actually need.
Equipment is often designed to do more that
what it is required to do in its actual operating
conditions. As maintainers, we should be very
careful about maintaining to design capabili-
ties. Instead, in most cases, we should main-
tain our equipment to deliver to operating
requirements. Maintenance done to ensure
equipment capacity greater than actually
needed is a waste of resources.
Similarly, avoid assigning multiple tasks to a
single failure mode. It’s wasteful and it makes
it hard to determine which task is actually
effective. Stick to the rule of a single, effective

task per failure mode as much as you can.
Only for very high consequence failure modes
should you consider having multiple, diverse
tasks to a single failure mode.
Most organisations have more maintenance
to do than resources to do it with. Use resourc-
es on unnecessary maintenance, and you risk
not completing necessary maintenance. And
not completing necessary maintenance, or
completing it late, increases the risk of fail-
ures.
And when that unnecessary maintenance
is intrusive it gets worse. Experience shows
that intrusive maintenance leads to increased
failures because of human error. This could
be simple mistakes. Or because of defective
materials or parts, or errors in technical docu-
mentation.
A lot of maintenance is done with the equip-
ment off-line. So doing unnecessary mainte-
nance can also increase production losses.
So make sure you remove unnecessary main-
tenance from your system. Make sure you
have a clear and legitimate reason for every
task in your maintenance program. Make sure
you link all tasks to a dominant failure mode.
And have clear priorities for all maintenance
tasks. That allows you to prioritise tasks. In the
real world, we are all resource-constrained.
Principle #9: Good maintenance
programs become better
maintenance programs
The most effective maintenance programs
are dynamic. They are changing and improv-
ing continuously. Always making better use of
our scarce resources. Always becoming more
effective at preventing those failures that
matter to our business.
When improving your maintenance program
you need to understand that not all improve-
ments have the same leverage:
First, focus on eliminating unnecessary main-
tenance tasks. This eliminates the direct
maintenance of labour and materials. But
it also removes the effort required to plan,
schedule, manage, and report on this work.
Second, change time-based overhaul or
replacement tasks into condition-based tasks.
Instead of replacing a component every so
many hours, use a condition monitoring tech-
nique to assess how much life the component
has left. And only replace the component
when actually required.
And third, extend task intervals. Do this based
on data analysis, operator and maintainer
experience. Or simply on good engineering
judgment. Remember to observe the results.
The shorter the current interval, the great-
er the impact when extending that interval.
For example, adjusting a daily task to week-
ly reduces the required PM workload for

that task by more than 80%. This is often
the simplest and one of the most effective
improvements you can make.
RCM FAQs
Before I wrap up this article, I wanted to
answer some of the most common FAQs
relating to reliability centered maintenance,
and these are:
What is reliability-centered
maintenance?
Reliability-centered maintenance (RCM) is
an internationally defined, structured deci-
sion-making process to develop or optimise a
Preventive Maintenance Program. RCM focus-
es on preserving system functions rather than
preserving equipment. The most fundamen-
tal requirement of any RCM process is that it
must adequately and completely answer the
following seven questions:
1. What are the functions and associated
design performance standards for the
asset in its current operating context?
2. In what way can the asset fail to fulfill its
functions?
3. What causes each possible functional
failure?
4. What happens when each function of
failure occurs?
5. In what way does each failure matter?
6. What should we do to predict or prevent
each failure?
7. What should we do if a suitable proactive
task cannot be found?
When done well, RCM will deliver highly effec-
tive and efficient PM programs, but imple-
menting RCM requires significant expertise
and resources. So you need to use it wisely.
RCM is defined through a set of internation-
al standards: SAE JA1011 titled “Evaluation
Criteria for Reliability Centered Maintenance
Processes” and SAE standard JA1012 titled “A
Guide to The Reliability Centered Maintenance
Standard”.
What is the difference between
RCM and FMEA?
Failure Mode Effects Analysis (FMEA) is a step
in the reliability centered maintenance (RCM)
process, but RCM does a lot more than just
analysing functional failures. It focuses on
defining functions, being clear on the oper-
ating context and selecting the right main-
tenance tasks based on the analysis of the
different failure modes.
I like to say that RCM is function-based,
Preventive Maintenance Optimisation (PMO)
is task-based and FMEA is equipment based,
but all good analyses are failure mode based!

What are the types of reliability-
centered maintenance?
Be very careful with the idea that there are
‘types of reliability centered maintenance’.
People do talk about classical RCM and accel-
erated RCM. Classical RCM is the RCM process
as originally defined by Nowland & Heap
and now documented in SAE JA1011 and SAE
JA1012. Accelerated RCM is an adaption of the
classical RCM process, and there are quite a
few variations – some are robust but others
are not. Buyer beware!
References
I wrote this article based on a number of key sources listed below (and throughout the arti-
cle). I strongly recommend getting yourself a copy of Moubray’s book on Reliability Centered
Maintenance if don’t already own a copy. And I’d definitely get the NAVSEA Reliability Centered
Maintenance (RCM) manual as it’s well-written and easy to understand:
• Moubray, J. (1997) Reliability Centered Maintenance Second Edition. Industrial Press. Available at: https://
www.amazon.com/Reliability-Centered-Maintenance-Second-John-Moubray/dp/0831131462.
• NAVSEA (2007) Reliability Centered Maintenance (RCM) Handbook [S9081-AB-GIB-010]. Available at: https://
www.amazon.com/NAVSEA-Reliability-Centered-Maintenance-RCM-Handbook-ebook/dp/B00U1UJPKK.
• Allen, T. M. (2001) ‘U.S. Navy Analysis of Submarine Maintenance Data and the Development
of Age and Reliability Profiles’. Available at: http://www.plant-maintenance.com/articles/
SubmarineMaintenanceDataRCM.pdf.
• White Paper (no date) ‘What is Reliability Centered Maintenance?’
• Wikipedia (2017) Reliability-centered maintenance. Available at: https://en.wikipedia.org/wiki/Reliability-
centered_maintenance
• NASA (2008) Reliability-Centered Maintenance Guide. Available at https://www.nasa.gov/sites/default/files/
atoms/files/nasa_rcmguide.pdf
What is the overall goal of RCM?
The overall goal of reliability-centered main-
tenance is to achieve the required reliability
levels for a system, at optimised maintenance
and cost levels by focusing on the preserva-
tion of key functions.

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