Root Cause Analysis

1
Root Cause Analysis

• Module 6

2
Learning Objectives
To learn some of the tools and techniquesused to
determine the root cause of the problem being
analyzed.
3
Topics

• Definition
• General rules
• Constraints
• Process flow for root cause
• Immediate corrective actions
• Root cause analysis techniques

4
Root Cause Analysis definition

• Root cause is the factor that caused a defect
  or nonconformance
• Root cause analysis (RCA) is a sequential and
  investigative process used to determine the root
  cause of the problem

5
General rules to perform root cause analysis

• Team effort
• The team must fully understand the problem
  prior to start the analysis
• Look beyond the obvious and immediate solutions
• Do not confuse symptoms and causes
• Symptom is a manifestation of a cause
• Cause is the factor which when removed, the
  problem is cured
• Use factual data

6
Constraints

• Time and schedule pressures
• Fire-fighting mode
• Attractiveness of an immediate fix
• Cost considerations
• Lack of thorough understanding of the problem
• Confusing symptoms versus causes

7
Constraints (continuation)

• Lack of documentation, data or information on
  how the problem occurred
• Lack of recompilation of the events that
  occurred before the problem.
• Failure to document data as evidence of the
  problem
• Lack of team approach
• Lack of training in performing root cause
  analysis

8
Root Causes Sources

• Some possible sources causing a problem are
• Inadequate knowledge of how the process works
• Inadequate knowledge of how the process should
  work
• Errors and mistakes in executing established
  procedures
• Inadequate procedures
• Inadequate steps and wasteful measures
• Variation in inputs to the process

9
Immediate Corrective Actions

• They are developed and implemented to cure,
  or alleviate the problem momentarily, while the
  root cause is investigated
• Immediate corrective actions are not
  necessarily root cause corrections
• Immediate corrective actions are needed to
  avoid major cost impact

10
Immediate Corrective Actions (continuation)

• Benefits
• It is quick
• Does not take too much effort to develop
• Inexpensive
• Keeps management happy
• It saves the process from being shut down

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Immediate Corrective Actions (continuation)

• Disadvantages
• Not process oriented
• Because of time constraints, it lacks thorough
  analysis
• Usually, it is one person opinion
• Misinterpreted cost effectiveness
• Often, lacks data and documentation

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Root cause analysis flow
PDCA
Identify the problem
RCA flow
Analyze the current situation
Isolated case?
no
Determine Root Cause(s)
yes
yes
no
Choose solutions action plan
yes
no
Implement solution
Check results (evaluate)
Act on learnings
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Root cause analysis techniques

• The most common methods used in root cause
  analysis are
• 5-whys, or Why-why analysis.
• Cause and effect diagram (covered in Module 3)
• Fault tree
• RCA process is extremely efficient when
  performed as a team effort.

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Why-why analysis

• Technique for determining the root cause or
  contributing causes of a problem.
• It shows the relationship of causes by
  repeatedly asking the question why?
• It usually, takes 5 levels of why? to
  determine the root cause

15
Why-why analysis (continuation)

• It organizes team thoughts
• It establishes priorities or contributing
  factors, or causes.
• The more arrows that point to a cause, the
  higher the priority may be

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Process for constructing a Why-why chart

• Assemble multifunctional team
• Use a large area board or a flip-chart
• Write the problem statement at the bottom
• The level 1 why is determined by answering
  the question why? To the problem statement.
• Write all the answers from the team on a line
  above the problem statement

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Process for constructing a Why-why
chart (continuation)

• The level 2 why is determined by answering
  the question why? to each of the answers on level
  1.
• Continue building the level 3, level 4, and
  level 5 question-answer relationships.
• Connect all answers as applicable
• It is the team decision to stop at level 5, or
  to continue, or even stop before level 5

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Process for constructing a Why-why
chart (continuation)

• The answers common to the last level of the
  analysis are the root causes to the problem
• Assign priorities to these root causes
• Proceed and develop a corrective action plan
  as discussed on Module 4.

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Why-why example
Clarify specification
Establish team to
Request supplier Corrective action plan
Review training module.
in the use of
Identify areas of
determine
QE to create summary
relief washers
vs
Limited access
Best chamfer
-
relief
Matrix acceptance criteria
chamfer relief to
Inspection practice
for type of fasteners
shop personnel
Not in the preferred supplier list
No measuring gauge
Available for relief
Chamfer inspection
Different acceptance
Relief chamfer
Inadequate supplier surveillance
Criteria for different
dimension
Type of fasteners
is not measured
Lack of
Requirement to use
Experience/
Supplier deficiency
Relief washers not
Procedure
Some areas have
Not familiar with
clear at shop level
not followed or
Limited access
requirements
followed incorrectly
Why?
Level 2
Did not insert
Collars break
-
off
Shop personnel do not understand requirements
Feeler gauges
feeler gauge all
Usage of appropriate tools
De
-
burring/chamfer
too easy not allowing
not used
around perimeter
Drill Blocks /
not performed
to seat properly
of head/collar
eggcups
Engineering
Drawing
Improper inspection
Poor quality
Lack/insufficient
Hand drilling
Customer Specification not followed
method
hardware
Relief chamfer

Problem
Defective fastener installation
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Fault Tree analysis

• It is a deductive procedure using the major
  functions that have inputs to a process
• It is very useful when using multifunctional
  team members
• The Tree-fault analysis identifies contributing
  causes within a functional hierarchy common to
  the process.

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Process for constructing a Fault Tree analysis

• Assemble a multifunctional team
• Use a large area board or a flip-chart
• Write the problem statement at the top
• Determine major functional groups
• Exercise team brainstorming and start listing
  potential tasks contributing to the problem

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Tree Fault example
Oversized Bushings
Quality Assurance
Manufacturing
Design Engineering
Operation instructions not clear
Oversize Holes Not detected via Audits
Engineering
Standard Tooling
Tooling
Holes Not Checked After Ream Operation
Drawing Tolerances May Not be Achievable For
current product configuration
Worn Tool Details. DJs Out of Tolerance.
Concentricity of Bushing Not Per Tool design
No Setup Procedure Nor Wear Limits for
Drill Bushing for Close Tolerance Holes
Major Contributor
.
Minor Contributor
.
No Impact
.
Under Investigation
.
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Summary
Performing thorough root cause analysis is a step
forward to process improvement. It is so
important to fix the correct cause of the
problem, otherwise these will recur, and any
accomplished gain will be lost.