REL103;01202004Slide 1

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 part failures on

the board?

What are the effects

of board failures on

the box?

What are the effects

of box failures on

the system?

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.)

Item Failure Mode End Effect

bulb dim light flashlight output dimno light no flashlight output

switch stuck closed constant flashlight outputstuck open no flashlight outputintermittent flashlight sometimes will not turn on

contact poor contact flashlight output dimno contact no flashlight outputintermittent flashlight sometimes will not turn on

battery low power flashlight output dimno power no flashlight output

How can it fail?

What is the effect? Note

that Next Higher Effect =

End Effect in this case.

Part

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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.)

Item Failure Mode End Effect Severity

bulb dim light flashlight output dim IIIno light no flashlight output II

switch stuck closed constant flashlight output Istuck open no flashlight output IIintermittent flashlight sometimes will not turn on III

contact poor contact flashlight output dim IIIno contact no flashlight output IIintermittent flashlight sometimes will not turn on III

battery low power flashlight output dim IIIno power no flashlight output II

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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.