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The P-F Interval According to NAVAIR 00-25-403 RCM Guideline.

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Presentation on theme: "The P-F Interval According to NAVAIR 00-25-403 RCM Guideline."— Presentation transcript:

1 The P-F Interval According to NAVAIR RCM Guideline

2 OMDEC IncSlide Number: 2Session 4Performance NAVAIR P-F Interval The following describes NAVAIR [1] methods based on the classic CBM: 1.Determining the P-F Interval, and 2.Determining the Inspection Interval [1] NAVAIR RCM GuidelineNAVAIR RCM Guideline

3 OMDEC IncSlide Number: 3Session 4Performance NAVAIR Methods for determining PF intervals: Laboratory testing (in conjunction with accelerated life testing (ALT)), Analytical methods Evaluation of in-service data - AE (Age Exploration), and engineering judgement based on inputs from operators and maintainer, (i.e. Classic RCM method) and Knowledge of the items design and of applications consisting of similar components. Note: NAVAIR does not provide details about the above methods in its guide.

4 OMDEC IncSlide Number: 4Session 4Performance PF used only for starting Inspection Interval The PM task interval is determined by using some fraction of the PF interval. This fraction will depend on the consequences of failure and the effectiveness of the proposed task. I = PF/n Where: I = Inspection interval PF = potential failure to functional failure interval n = number of inspections in the PF interval

5 OMDEC IncSlide Number: 5Session 4Performance Determining n n = ln (P acc ) / ln (1-θ) Where: θ = Probability of detecting a potential failure with one occurrence of the proposed On Condition task, assuming the potential failure exists P acc = Acceptable probability of failure Note: θ can only be determined practically in a LRCM program that tracks CBM hits and misses.

6 Error in the Guide The next slide illustrates an error by NAVAIR regarding the P-F interval. It is a commonly held misconception …

7 OMDEC IncSlide Number: 7Session 4Performance OPERATING AGE A FUNCTIONALFAILURE POTENTIALFAILURE B C DEFINED POTENTIAL FAILURE CONDITION Inspection Interval Functional Failure: PRACTICAL? TASK INTERVAL PRACTICAL? III Task Development PF Interval ON CONDITION TASK DEFINED FUNCTIONAL FAILURE CONDITION Functional Capability

8 OMDEC IncSlide Number: 8Session 4Performance OPERATING AGE A FUNCTIONALFAILURE POTENTIALFAILURE B C DEFINED POTENTIAL FAILURE CONDITION Inspection Interval Functional Failure: PRACTICAL? TASK INTERVAL PRACTICAL? III Task Development PF Interval ON CONDITION TASK DEFINED FUNCTIONAL FAILURE CONDITION Functional Capability Implies that functional capability will drop off as the system approaches a potential failure state (point B). In fact, in most cases, especially in complex systems, the equipment's functions remain fully operational at the potential failure point

9 OMDEC IncSlide Number: 9Session 4Performance OPERATING AGE A FUNCTIONALFAILURE POTENTIALFAILURE B C DEFINED POTENTIAL FAILURE CONDITION Inspection Interval Functional Failure: PRACTICAL? TASK INTERVAL PRACTICAL? III Task Development PF Interval ON CONDITION TASK DEFINED FUNCTIONAL FAILURE CONDITION Functional Capability Condition In the original on-condition model by Nowlan and Heap, and in Moubray's book "RCM II", the vertical axis is correctly labelled "Condition or Failure Resistence

10 OMDEC IncSlide Number: 10Session 4PerformanceConclusion The P-F Interval is a good, but subjective, first approximation developed during an RCM analysis in the absence of data based on the recollection by the analysts of potential and functional failures that have occurred. Age exploration techniques (e.g. EXAKT and LRCM) during the In-Service (IS) phase of operation should be used to confirm inspection frequencies and refine predictive models for the continuous improvement in Remaining Useful Life Estimation (RULE).


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