This document provides an overview of Failure Mode and Effects Analysis (FMEA). It discusses how FMEA was developed in the aerospace industry in the 1960s and later adopted by the automotive industry. The FMEA process involves identifying potential failure modes, their causes and effects, then calculating a risk priority number (RPN) based on severity, occurrence, and detectability ratings. The document provides an example FMEA on credit card transaction approval/rejection, showing how failure modes are analyzed, RPNs calculated, and mitigation methods identified to reduce risk.

1. Failure Mode and Effects Analysis
ASQ-SCV May 19, 2000
Douglas Hoffman
Software Quality Methods, LLC.
24646 Heather Heights Place
Saratoga, California 95070-9710
Phone 408-741-4830
Fax 408-867-4550
Copyright © 2000, Software Quality Methods, LLC. No part of these graphic overhead slides may
be reproduced, or used in any form by any electronic or mechanical duplication, or stored in a
computer system, without written permission of the author.
Douglas Hoffman Copyright © 2000, SQM, LLC. 1
What is FMEA?
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2. Background
• Analysis of failure modes, causes, and effects
• Aerospace in 1960’s
• QS9000 in 1993 (automotive)
• Analysis per function, per failure mode
• RPN = Severity X Occurrence X Detectability
• Action/Results to reduce risk
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FMEA Process
• Identify Function, Failure Modes, and Cause
• Then Severity, Occurrence, and Detectability
• Compute RPN
• Decide cut-off
• Identify Mitigation methods
• Adjust Severity, Occurrence, or Detectability
and RPN
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3. Example
• Credit card check
• Results
– Approve
– Reject
– Cancel Card
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Severity
• What consequence if failure happens
• 1 to 10 Scale
• 1 means no consequence
• No set categories
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4. Occurrence
• Likelihood the failure happens
• 1 to 10 Scale
• 1 means not likely
• No set categories
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Detectability
• Likelihood of missing a failure
• 1 to 10 Scale
• 1 means it will be noticed
• No set categories
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5. Example
• Functions
– Verify credit availability
• Failure Modes
– Accepts over limit (OL)
– Rejects under limit (UL)
– Calls police in error (CP)
• Causes
– Software error (SE)
– Input error (IE)
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Example (continued)
• Severity • Occurrence • Detectability
– OL = 6 – OL/SE = 4 – OL/SE = 1
– UL = 4 – OL/IE = 7 – OL/IE = 1
– CP = 9 – UL/SE = 4 – UL/SE = 6
– UL/IE = 7 – UL/IE = 6
– CP/SE = 3 – CP/SE = 9
– CP/IE = 2 – CP/IE = 9
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6. FMEA Table
Failure
Function Mode/Cause Severity Occurrence Detectability RPN
OL/SE 6 4 1 24
Credit
Check
OL/IE 6 7 1 42
UL/SE 4 4 6 96
UL/IE 4 7 6 168
CC/SE 4 3 6 72
CC/IE 4 2 6 48
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Mitigation
• Actions to reduce risk
– Severity
– Occurrence
– Detectability
• New RPN computed
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7. Adjusted FMEA
Failure
Mitigation Severity Occurrence Detectability RPN
Mode/
Cause
OL/SE Test 6 4 1 24
OL/IE Automate 6 2 1 12
UL/SE Test 4 4 3 48
UL/IE Automate 4 2 6 48
CC/SE Test 4 3 3 36
CC/IE Automate 4 2 6 48
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Metric Data Computations
• What numeric types are Severity,
Occurrence, and Detectability?
• What are appropriate computational
functions for the data types?
• How accurate is our measurement of each
metric? (What is the margin of error?)
• What do RPN computations mean?
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8. Conclusions
• Analysis is Good
• FMEA framework supports
analysis
• Don’t take it too far
• Be wary of statistics
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