FAILURE MODE EFFECT ANALYSIS
CHAPTER 1
INTRODUCTION
The FMEA is an analysis procedure by which each potential failure mode in a system is
analysed to determine the results or effects thereof on the system and to classify each potential
failure mode according to its severity. The initial FMEA should be done early in the conceptual
phase when design criteria, mission requirements, and preliminary designs are being developed
to evaluate the design approach and to compare the benefits of competing design
configurations. It involves reviewing as many components, assemblies, and subsystems as
possible to identify failure modes, and their causes and effects. For each component, the failure
modes and their resulting effects on the rest of the system are recorded in a specific FMEA
worksheet.
A few different types of FMEA analyses exist, such as:



Functional
Design
Process
An FMEA is often the first step of a system reliability study. The FMEA will provide quick
visibility of the most obvious failure modes and identify potential single failure points, some
of which can be eliminated with minimal design effort. As the mission and design definitions
become more refined, the FMEA can be expanded to successively more detailed levels. When
changes are made in system design to remove or reduce the impact of the identified failure
modes, the FMEA must be repeated for the redesigned portions to ensure that all predictable
failure modes in the new design are considered.
There are two primary approaches for accomplishing an FMEA. One is the hardware approach
which lists individual hardware items and analyses their possible failure modes. The other is
the functional approach which recognizes that every item is designed to perform a number of
functions that can be classified as outputs. The outputs are listed and their failure modes
analysed.
1. Functional FMEA Approach - The functional approach is used when hardware items
cannot be uniquely identified. Each identified failure mode is assigned a severity
classification which can be utilized during design iterations to establish priorities for
corrective actions. It should be the first FMEA to be performed and should be updated
throughout the design iteration process or as corrective actions are implemented.
2. Hardware FMEA Approach - The hardware approach is normally used when
hardware items can be uniquely identified from schematics, drawings, and other
engineering and design data. The hardware approach is normally utilized in a part level
up fashion. Each identified failure mode is assigned a severity classification which will
be utilized during design to establish priorities for corrective actions. The hardware
FMEA should commence after the design process has delivered a schematic diagram
with all system items or parts defined. This is usually the final FMEA for the design
but should be updated whenever design changes or corrective actions occur.
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For complex systems, a combination of the functional and hardware approaches may be
considered. The FMEA may be performed as a hardware analysis, a functional analysis, or a
combination analysis and is ideally initiated at the part, circuit or functional level and proceeds
through increasing indenture levels until the FMEA for the system is complete.
A successful FMEA activity helps identify potential failure modes based on experience with
similar products and processes. It is widely used in development and manufacturing industries
in various phases of the product life cycle. Effects analysis refers to studying the consequences
of those failures on different system levels.
Sometimes FMEA is extended to FMECA (Failure Mode Effects and Criticality Analysis) to
indicate that criticality analysis is performed too. FMEA is a core task in reliability
engineering, safety engineering and quality engineering. The FMECA is a design tool used to
systematically analyse postulated component failures and identify the resultant effects on
system operations.
The analysis is sometimes characterized as consisting of two sub-analyses, the first being the
failure modes and effects analysis, and the second, the criticality analysis. FMEAs can be
performed at the system, subsystem, assembly, subassembly or part level. The FMECA should
be a living document during development of a hardware design.
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CHAPTER 2
REQUIREMENTS
2.1 Hardware Requirements
o Bill of Materials
2.2 Software Requirements
o Visual Basic for Applications
o Microsoft Excel
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CHAPTER 3
IMPLEMENTATION
The Failure Mode Effect Analysis tool template should consist of the following discrete steps
before creating the worksheet to perform the analysis:

Define the System to be Analysed : A complete system definition which includes
identification of internal functions, performance of all items at all levels, failure
definitions must be provided to the analyst.

Construct Block Diagrams: Functional and reliability block diagrams which illustrate
the operation, interrelationships of functional entities for each items used in the system.
A uniform numbering system to trace hierarchy functional system breakdown order is
necessary and will rapid tracking through all levels of indenture.

Identify Potential Failure Items: Define and describe the failure effects of the item
and all predictable failures modes associated with it. If the failure mode has one cause,
all probable independent causes for each failure mode should be identified and
described.
3.1 KEY TASKS PERFORMED:
Studied and understood the concept of FMEA and used visual basic for applications to design
a tool template for the Bill of Materials (BoM) to perform Failure Mode Analysis using Excel
worksheets. The datasheets, BOM(s), schematics provided by the system engineers were
studied and the following requirements to design the tool template were formulated:
1.
2.
3.
4.
5.
6.
7.
8.
The tool shall take inputs from the BOM(s), schematics and the master tables.
The tool shall produce an output based on the following inputs i.e. the FMEA sheet.
The tool shall have the facility to configure BOM fields & contain a format to read.
The tool shall have the facility to read the BOM(s).
The tool shall prepare a unique component list from the read BOM(s).
The tool shall have the facility to read the schematics.
A schematic shall be used to refer to create the tool.
The schematic shall contain information about reference designator, function name,
properties, description and the type of component used.
9. The failure mode ratio shall be computed by taking the respective failure mode by the
total number of times the component has been used.
10. The tool shall contain the fields listed in table 1 for the analysis of the FMEA process.
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11. The tool shall provide a facility to configure additional fields to appear in FMEA.
12. The tool shall provide a facility to delete optional fields from the FMEA.
13. The tool shall consist of a field called level with different levels representing different
component levels. Namely:
Level number
1
2
3
4
REPRESENTING COMPONENT LEVEL
LRU
BOARD NAME
FUNCTION AND SUB-FUNCTION
COMPONENT
14. The tool shall have the facility to configure the master table.
15. The tool shall contain a master table for FIT values as defined in table 2 in the annexure.
16. The tool shall provide a facility to configure the FIT values used in the master tables.
17. The tool shall contain a master table for next effects and end effects as defined in table
3 in the annexure.
18. The tool shall contain a master table for failure mode and its distribution as defined in
table 4 in the annexure.
19. The tool shall provide a facility to configure the following parameters for a list of
components listed from the BOM:





Component type
Designator
Component Description
Part Number
Pin(s)
20. The tool shall provide a facility to auto complete the local effect field based on already
entered values.
21. The tool shall provide a facility to auto complete the next effect field along with a dropdown menu to choose within the list of next effects based on already entered values.
22. The tool shall provide a facility to auto complete the end effect field along with a dropdown menu to choose within the list of end effects based on already entered values.
23. The tool shall have the facility to read and copy values of the part number, component
type, Component Description from the BOM(s).
24. The following fields in the tool shall contain information given by the manufacturer:









Function name/ Description
Component Category
Probability of Failure
Failure Modes
FIT values
Failure Mode Ratio
Compensating Provisions
Detection Methods
Detection Mechanisms
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

Pin(s)
Recommendation/ Remarks
The following table is the model worksheet for Failure Mode Effect Analysis:
The following table is the required FMEA worksheet for the Bill of Materials produced by
L&T Technology Services:
Table1:
FIELDS
DESCRIPTION
TYPE OF ENTRY
Levels
Provides different functioning levels
Automated
Failure Mode Identifier
Provides a unique designator for each
failure mode.
Automated
Function Name/
Description
Provides the name of the circuit under Automated
analysis. At the sub-line replaceable
unit (LRU), this refers to the block
diagram on the circuit card assembly
(CCA) or another circuitry block being
analyzed.
Component Category
Category of the component being
analyzed.
Automated
Reference Designator
Provides a unique reference designator
to the functional block on the CCA
block diagram.
Automated
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Pins
Identifies the connector pin that the
part is routed to.
Automated
Component Description
Description about the component
Automated
Component Part Number
Manufacture part number for the
component/ item being analyzed.
Automated
Failure Mode
The detailed data to understand the
failures at the component level.
The actual quantity or percentage of
each specific failure by source.
Manual
Failure Rate
Provides the failure rate of the
component derived from the reliability
prediction. It is expressed in terms of
failure per million operating hours.
Semi- Automated
Fit Value
It is a standard industry value defined
as the failure rate per billion hours.
Automated
Failure Mode Ratio
Calculated by multiplying component
failure rate by the applicable failure
mode percentage.
Automated
Mode Failure Rate
( Mode Distribution * FIT Value )
Automated
Mission Phase
Time at which the failure might occur.
Manual
Operation Mode
Modes of operation at the higher level.
Manual
Local effect
The failure effect as it applies to the Manual
item under analysis.
Next Effect
The failure effect as it applies at the Semi- Automated
next higher indenture level.
The failure effect at the highest Semi- Automated
indenture level or total system.
Mode Distribution
End Effect
Compensating Provisions
Recommendation/
Remarks
Manual
Identify corrective design or other Automated
actions required to eliminate the failure
or control the risk.
Provides the recommendations and Automated
remarks.
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Probability of Detection
The means of detection of the failure
mode by maintainer, operator or built
in detection system, including
estimated dormancy period.
Automated
Detection mechanisms
Describes the methods by which
occurrence of failure mode is detected
by the operator or maintenance
personnel.
Automated
Severity
The consequences of a failure mode.
Severity considers the worst potential
consequences of a failure, determined
by the degree of injury, property
damage, system damage and time lost
to repair the failure.
Manual
Occurrence
Probability of occurrence of the
failure.
Manual
The following are the additional fields that can be included into the FMEA Worksheet based
on the requirement of the failure analysis:
i)
ii)
iii)
iv)
v)
vi)
Failure: The loss of a function under stated conditions.
Failure mode: It may generally describe the way the failure occurs.
Failure cause: Defects in requirements, design, process, quality control, which are
the underlying cause or sequence of causes that initiate a process that leads to a
failure mode over a certain time.
Failure effect: Immediate consequences of a failure on operation, function or
functionality, or status of some item.
Indenture levels: An identifier for system level and thereby item complexity.
Complexity increases as levels are closer to one.
Risk Priority Number (RPN): Severity * Probability * Detection.
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CHAPTER 4
RESULTS
4.1 FAILURE CLASSIFICATION:
Each failure mode should be evaluated in terms of the worst potential consequences which may
result. A code will be assigned describing the worst possible incidence of this failure. This code
is the severity classification code. Severity classifications are assigned to provide a qualitative
measure of the worst potential consequences resulting from design error or item failure. A
severity classification is assigned to each identified failure mode and each item analysed in
accordance with the loss statement below. Where it may not be possible to identify an item or
a failure mode according to the loss statements in the four categories below, similar loss
statements based upon loss of system inputs or outputs can be developed and included in the
FMEA. Severity classification categories which are consistent with various military standards
are defined as follows:




Category 1 - Catastrophic - A failure which may cause death or weapon system
loss.
Category 2 - Critical - A failure which may cause severe injury, major property
damage, or major system damage which will result in mission loss.
Category 3 - Marginal - A failure which may cause minor injury, minor property
damage, or minor system damage which will result in delay or loss of availability
or mission degradation.
Category 4 - Minor - A failure not serious, enough to cause injury, property
damage, or system damage, but which will result in unscheduled maintenance or
repair.
4.2 METHODS:
 Failure Detection Method - Describe the methods by which occurrence of a failure
mode is detected by the operator or maintenance personnel. The failure detection
means, such as visual or audible warning devices, automatic sensing devices, sensing
instrumentation, other unique indications, or none, should also be identified here.
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 Failure Isolation Method - Describe the most direct procedure that allows an operator
or maintenance personnel to isolate the failure. The failure being considered in the
analysis may be of lesser importance or likelihood than another failure that could
produce the same symptoms but must still be considered. Fault isolation procedures
require a specific action or series of actions by an operator, followed by a check or cross
reference either to instruments, control devices, circuit breakers, or combinations
thereof. This procedure is followed until a satisfactory course of action is determined.
 Failure Compensation Method - Identify corrective design or other actions required
to eliminate the failure or control the risk. This step is required to record the true
behaviour of the item in the presence of a failure. The analyst should describe design
compensating provisions that will:
 Nullify the effects of a failure
 Control or deactivate system items to halt generation or propagation of failure
effects
 Activate backup or standby items or systems. Design compensating provisions can
include redundant items that allow continued and safe operation, safety or relief
devices such as monitoring or alarm provision.
4.3 RANKING CRITICALITY:
The purpose of the Criticality Analysis is to rank each potential failure mode identified by the
FMEA according to the combined influence of severity classification and its probability of
occurrence based upon the best available data. It is completed after the local, next higher level
and end effects of a failure have been determined by the FMEA.
4.3.1 QUALITATIVE APPROACH :
Failure modes identified in the FMEA are assessed in terms of probability of occurrence levels,
when specific parts configuration or failure rate data -re not available. Individual failure mode
probabilities of occurrence are grouped into distinct, logically defined levels, which establish
the qualitative failure probability level for entry into the appropriate CA worksheet column.
Probability of occurrence levels are very subjective and may require in-depth knowledge of the
system to make an educated judgement. A good set of guidelines are defined as follows:
Level A– Frequent- A high probability of occurrence during the item operating time interval.
High probability may be defined as a single failure mode probability greater than 0.20 of the
overall probability of failure during the item operating time.
Level B- Reasonably probable- A moderate probability of occurrence during the item
operating time interval. Probable may be defined as a single failure mode probability of
occurrence which is more than 0.10 but less than 0.20 of the overall probability of failure during
the item operating time.
Level C– Occasional- An occasional probability of occurrence during item operating time
interval. Occasional probability may be defined as a single failure mode probability of
occurrence which is more than 0.01 but less than 0.10 of the overall probability of failure during
the item operating time.
Level D– Remote- An unlikely probability of occurrence during item operating time interval.
Remote probability may be defined as a single failure mode probability of occurrence which is
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more than 0.001 but less than 0.01 of the overall probability of failure during the item operating
time.
Level E- Extremely Unlikely- A failure whose probability of occurrence is essentially zero
during the item operating time interval, Extremely unlikely may be defined as a single failure
mode probability of occurrence which is less than 0.001 of the overall probability of failure
during the item operating time.
4.3.2 QUANTITATIVE APPRQACH:
Failure modes identified in the FMEA are assessed and ranked in terms of a criticality number
which is computed using failure rate and probability of occurrence data. The failure rate data
source used for the quantitative approach to CA should be the same as that used during the
reliability prediction.
Failure Rate- When a qualitative CA is performed, failure modes are assessed in terms of
probability of occurrence, the failure probability of occurrence level must be shown in this
column. When failure rate data are available, a quantitative CA can be performed and criticality
numbers may be calculated. In this case, the data source of the failure rates used in each
calculation shall be listed in this column. When a failure probability is listed, the remaining
columns are not required and the next step will be the construction of a criticality matrix.
Failure Effect Probability- The beta values are the conditional probability that the failure
effect will result in the identified criticality classification, given that the failure mode occurs.
The beta values represent the analyst's judgment as to the conditional probability the loss will
occur and should be quantified in general accordance with the values in the table.
FAILURE EFFECT
BETA VALUE
Actual Loss
1.00
Probable Loss
> 0.10 to < 1.00
Possible Loss
> 0 to 0.10
No Effect
0
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CONCLUSION
The FMEA template consists of columns that analyses the failure effects and propose suitable
solutions to overcome these failures. The purpose of FMEA is identify potential failure modes
of components. FMEA increases the reliability of a system along with a complete
understanding of all the items present in the product along with their failures and effective
methods to reduce these failures. After analyzing the Bill of Materials and we can conclude
that creating the FMEA worksheet helps in the following ways:

















Acts as a catalyst for teamwork and idea exchange between functions.
Collects information to reduce future failures, capture engineering knowledge.
Ensures that the failures have been eliminated or the risk is reduced to acceptable level.
Early identification and elimination of potential failure modes.
Emphasizes on problem prevention.
Helps with the design choices.
Improves company image and competitiveness.
Improves production yield.
Improves the quality, reliability, and safety of a process.
Increase in user satisfaction.
Maximizes profits.
Minimize the likelihood of failures.
Minimizes late changes and associated cost.
Reduces impact on company profit margin.
Reduces system development time and cost.
Reduces the possibility of same kind of failure in future.
Reduces the potential for warranty concerns.
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References
1. MILHDBK-217
2. NPRD-91
3. Failure Mode/ Mechanism distribution by the Reliability Analysis Centre (RAC)
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Annexures
Table2:
The values for the table below will be provided by the system engineers.
DEVICE
NAME/TYPE
FIT VALUE
Table3:
The contents in the next effect column are- The different possible next effects corresponding
to the different end effects caused as a result of those next effects.
NEXT EFFECT
END EFFECT
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A1
E1
E2
E3
A2
E1
E4
E5
A3
E3
E6
A4
E2
Table4:
The following values are some of the standard Failure Mode Distribution ratios:
DEVICE TYPE
FAILURE MODES
Accumulator
Leaking
Seized
Worn
Contaminated
FAILURE
MODE
PROBABILITY
0.47
0.23
0.20
0.10
Actuator
Spurious
Position Change Binding
Leaking
Seized
0.36
0.27
0.22
0.15
Adapter
Physical Damage
Out of Adjustment
Leaking
0.33
0.33
0.33
Alarm
False Indication
Failure to Operate on Demand
Spurious Operation
Degraded Alarm
0.48
0.29
0.18
0.05
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Antenna
No Transmission
Signal Leakage
Spurious Transmission
0.54
0.21
0.25
Battery, Lithium
Degraded Output
Start-up Delay
Short
0.78
0.14
0.06
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