Introduction to FMECA

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Introduction to FMECA

• What is a FMECA?
• An Analysis technique which facilitates the
  identification of potential design problems by
  examining the effects of lower level failures on
  system operation.

Obviously, a major malfunction.
- Stephen A Nesbitt NASA
Public Affairs Officer
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Why is it Important?

• Provides a basis for identifying root failure
  causes and developing effective corrective
  actions
• Identifies reliability/safety critical components
• Facilitates investigation of design alternatives
  at all stages of the design
• Provides a foundation for other maintainability,
  safety, testability, and logistics analyses

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Definitions

• FMECA - Failure Mode, Effects, and Criticality
  Analysis.
• FMEA - Failure Mode and Effects Analysis.
• COMPENSATING PROVISIONS - Actions available or
  that can be taken to lessen or eliminate the
  effect of a failure on a system.
• NEXT HIGHER EFFECT - The consequence a failure
  mode has upon the operation, function, or status
  at the next higher level of assembly.
• END EFFECT - The consequence a failure mode has
  upon the operation, function, or status at the
  highest level of indenture.

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How is it Done?
What are the effects of box failures on the
system?
What are the effects of board failures on the
box?
What are the effects of part failures on the
board?
Note This is a bottoms up example.
Top down examples are possible.
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Simple Example Flashlight
This flashlight is for use by special operations
forces involved in close combat missions
(especially hostage rescue) during low
visibility conditions in urban areas. The light
is to mounted coaxially with the individual's
personal weapon to momentarily illuminate and
positively identify targets before they are
engaged. The exterior casing including the
transparent light aperture are from an existing
ruggidized design and can be considered immune
to failure.
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Simple Example Flashlight (cont.)
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Severity

• SEVERITY classifies the degree of injury,
  property damage, system damage, and mission loss
  that could occur as the worst possible
  consequence of a failure. For a FMECA these are
  typically graded from I to IV in decreasing
  severity.
• The standard severities defined in MIL-STD1682
  may be used or equipment specific severities may
  be defined with customer concurrence
  (recommended).

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Simple Example Flashlight (cont.)

• Severity
• Severity I Light stuck in the on condition
• Severity II Light will not turn on
• Severity III Degraded operation
• Severity IV No effect

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Simple Example Flashlight (cont.)
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Criticality

• CRITICALITY is a measure of the frequency of
  occurrence of an effect.
• May be based on qualitative judgement or
• May be based on failure rate data

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Simple Example Flashlight (cont.)
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Simple Example Flashlight (cont.)
Can circled items be designed out or
mitigated? (There may be others that need to
addressed also.)
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Integrated FMECA

• FMECAs are often used by other functions such as
  Maintainability, Safety, Testability, and
  Logistics.
• Coordinate your effort with other functions up
  front
• Integrate as many other tasks into the FMECA as
  possible and as make sense (Testability, Safety,
  Maintainability, etc.)
• Integrating in this way can save considerable
  cost over doing the efforts separately and will
  usually produce a better product.
• If possible, use the same analyst to accomplish
  these tasks for the same piece of hardware. This
  can be a huge cost saver.

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FMECA Facts and Tips

• FMECAs should begin as early as possible
• This allows the analyst to affect the design
  before it is set in stone.
• If you start early (as you should) expect to have
  to redo portions as the design is modified.
• FMECAs take a lot of time to complete.
• FMECAs require considerable knowledge of system
  operation necessitating extensive discussions
  with software/hardware Design Engineering and
  System Engineering.
• Spend time developing groundrules with your
  customer up front.