The concept of functions
and failures in modern maintenance management is very important. You
may already be familiar with Failure Modes & Effects Analysis (FMEA),
since it is a well-documented and established technique. However when
used as a tool in to determine maintenance through RCM, the difference
in the two basic approaches to FMEA need to be understood;
* equipment approach, which lists each item and analyses their possible
failure modes (bottom up),
* functional approach, which recognises that every item is designed
to perform a function or number of functions.
These functions are identified and the failure modes resulting in
loss of function are analysed (top down).
It is functional FMEA that is crucial to the success of understanding
the equipment and to determine the most applicable and effective maintenance.
To carry out a functional FMEA the consequences of loss of function
(functional failure) need to be known. To achieve this, the effects
of loss of function(s) of the item, component or system needs to be
identified and understood and hence the functions themselves need
to be defined.
The following light-hearted example serves to highlight the Functions,
Functional Failures, Failure Modes, Effects and Consequences in an
FMEA worksheet.
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System:
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Facility: STARSHIP
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Compiled by: Scotty
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Sheet 1
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FMEA
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Equipment:
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Name: USS ENTERPRISE
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Reviewed by: 1st
Officer Spock
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Worksheet
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Component:
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Tag No. NCC 1701-D
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Approved by: James T. Kirk
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of
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Function |
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Functional
Failure |
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Failure Mode |
Local Effect |
System Effect |
Consequence |
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1
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TO ACHIEVE 5 YEAR MISSION
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A
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ACHIEVES LESS THAN 5 YEAR MISSION
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1
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NOT SYNDICATED TO ENOUGH TV COMPANIES
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REVENUES DROP, CREW AUDITION FOR
DIFFERENT JOB
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TV COMPANY SCREENS THE X-FILES
INSTEAD
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Production
Critical
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B
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ACHIEVES LONGER THAN 5 YEAR MISSION
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1
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SYNDICATED TO LOTS OF TV COMPANIES
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REVENUE INCREASES, CREW PUT ON
WEIGHT THROUGH RICH FOOD AND EASY LIVING
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MORE SCRIPTS WRITTEN, NEXT GENERATION
CREATED
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Safety
Critical
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2
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TOO MANY MERCHANDISNG OPPORTUNITES
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MANUFACTURERS OF T-SHIRTS, KEY
RINGS AND PASTIC TOYS WORKING FLAT OUT
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YOU TOO CAN HAVE A MOBILE PHONE
THAT FLIPS UP LIKE CAPTAIN KIRK’S
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No
Consequence
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3
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TOO MANY SUCCESSFUL MOVIES
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2
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TO SEEK OUT NEW WORLDS & NEW
CIVILISATIONS
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A
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DOES NOT SEEK OUT ANY WORLDS OR
CIVILATIONS
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1
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UNABLE TO NAVIGATE
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BEARINGS NOT AVAILABLE
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NICK LEASON JAILED
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Production
Critical
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B
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SEEKS OUT OLD WORLDS AND CIVILISATIONS
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1
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TOO MANY REPEATS ON TV
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EPISODES GET VERY REPETATIVE
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PEOPLE WATCH THE X-FILES INSTEAD
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Production
Critical
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3
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TO BOLDLY GO WHERE NO MAN HAS GONE
BEFORE
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A
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DOES NOT GO
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1
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DILITHIUM CRYSTALS EXHAUSTED
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WARP DRIVE TRIPS ON LOW ION FLOW
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SWITCH TO IMPULSE POWER
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Safety
Critical
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2
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DRIVE WARPED
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ENGINE TEMPERATURE RISES: ALARM
ANNUNCIATED
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ANNOUNCMENT THAT "SHE CAN’T
TAKE MUCH MORE CAPTAIN"
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Safety
Critical
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B
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GOES TIMIDLY
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1
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ANALYSED SEPARATELY
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C
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GOES WHERE MAN HAS GONE BEFORE
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1
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SEE 2.B.1
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Having established the functions,
functional failures, failure modes and their consequences the next step
is to determine which of the six basic maintenance strategies would
be applicable and effective to prevent or mitigate the consequences
of the failure;