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Unit III Module 4 - Hard Time Task
HOW TO PERFORM RCM Module 4 HARD TIME TASK "Copyright 2002, Information Spectrum, Inc. All Rights Reserved."
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Unit III Module 4 - Hard Time Task
Topics: Introduction Introduction Task Development Review and summary
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Unit III Module 4 - Hard Time Task
Module Objective: Introduction This module will provide information for evaluating and developing Hard Time tasks. 1. Identify when a Hard Time task is appropriate 2. Show how to develop a Hard Time task for a given failure mode. 3. Show how to determine an appropriate task interval for a Hard Time task. -403, 3.5.6
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Unit III Module 4 - Hard Time Task
TASK DEVELOPMENT
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Unit III Module 4 - Hard Time Task
Definition: Task Development Hard Time Task - The scheduled removal of an item or a restorative action at a specified age/usage limit to prevent functional failure. -403, 1.3, 3.5.6
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Unit III Module 4 - Hard Time Task
Questions: Task Development Does the item have a time or usage related wear-out age? Do an acceptable percentage of items survive to the wear out age? Can a task be developed that reduces the probability of failure to an acceptable level? Is the task and required interval practical? -403, 3.5.6
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Unit III Module 4 - Hard Time Task
Wear Out: Task Development Described as increase in conditional probability of failure with age TIME WEAR OUT REGION CONDITIONAL PROBABILITY OF FAILURE Slope Of Curve Determines Wear Out -403, 3.5.6
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Unit III Module 4 - Hard Time Task
Wear Out: Task Development Not all items wear out Some items show well defined wear out age where rapid increase in probability of failure occurs Other items may show steadily increasing conditional probability of failure that may support a hard time limit. Other items may not show wear out at all -403, 3.5.6
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Unit III Module 4 - Hard Time Task
Survival to Wear Out Age: Task Development Task intervals for items exhibiting age related wear out characteristics typically stated in terms of Life Limits Safe Life Limit Economic Life
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Unit III Module 4 - Hard Time Task
Survival to Wear Out Age: Safe Life Limit: Task Development Safe life limits Imposed only on items whose failure modes have safety consequences Item must survive: to age below which no failures are expected to occur or, where probability of survival meets program criteria SAFE LIFE LIMIT CONDITIONAL PROBABILITY OF FAILURE AGE -403, 3.5.6 1.0 PROBABILITY OF SURVIVAL AGE
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Unit III Module 4 - Hard Time Task
Survival to Wear Out Age: Task Development 1.0 PROBABILITY OF SURVIVAL -403, 3.5.6, Appendix B 100 % Survival to this age AGE
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Unit III Module 4 - Hard Time Task
Safe Life Limit: Task Development SAFE LIFE LIMIT CONDITIONAL PROBABILITY OF FAILURE AGE 1.0 -403, 3.5.6
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Unit III Module 4 - Hard Time Task
Survival to Wear Out Age: Task Development Economic Life Used for items whose failure modes have only Economic/Operational Consequences Warranted for item if it is cost effective to remove before it fails Set to maximize item’s useful life/minimize overall cost ECONOMIC LIFE LIMIT CONDITIONAL PROBABILITY OF FAILURE AGE -403, 3.5.6, Appendix B 1.0 PROBABILITY OF SURVIVAL AGE
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Unit III Module 4 - Hard Time Task
Economic Life Limit: Task Development CONDITIONAL PROBABILITY OF FAILURE ECONOMIC WEAR OUT AGE 1.0 -403, 3.5.6 AGE
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Unit III Module 4 - Hard Time Task
Task Interval: Task Development Based on age to wear out For task to be effective: Safety: Task Interval must reduce probability of failure to acceptable level Pact < Pacc Non-safety: Task interval must produce a cost effective task -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Task Interval: Task Development Methods typically used to determine wear out ages and task intervals: Failures with Safety Consequences: Statistical analyses (e.g., Weibull analysis) Fatigue or other testing to failure Fatigue analysis Failures with Non-Safety Consequences: Above plus Economic trade-off analysis -403, 3.5.6, 2.5, 2.9, Appendix B
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Unit III Module 4 - Hard Time Task
Weibull Analysis: Task Development Statistical technique using failure data to calculate accurate failure predictions How it is used: Plot failure data Determine various parameters that describe the failure data Use the parameters to determine if a hard time task is appropriate and at what interval it should be done -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Weibull Analysis: Task Development -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Fatigue Testing: Task Development Used to determine wear out age or safe life limits for components that must operate without failure for a certain amount of time How it is used: One or more components are tested to failure Estimate of earliest failure of one item in population is made. May be combined with Weibull or other statistical analysis or used with established safety factor -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Fatigue Analysis: Task Development Used to determine wear out age or safe life limits for components that must operate without failure for a certain amount of time How it is used: Mathematical analysis is conducted to determine Life to crack initiation and growth to critical crack size The calculated life to crack initiation is typically divided by a safety factor to obtain the hard time task interval for primary structure Some less critical applications may also include part of the crack-growth life in the Hard time interval -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Economic Trade-off Analysis: Task Development Conducted when working with non-safety related failure modes Method compares cost of the hard time task to the cost of allowing a failure to occur Analytical methods provided in Appendix C of NAVAIR Again… Correct application of numerical methods is the responsibility or each analyst/RCM team -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Estimating Methods: Task Development Methods for estimating task interval when exact data is not available: Use manufacturer’s recommended service life Base new task on an existing effective maintenance task Use engineering judgement based on similar components in similar applications Age exploration should be used to refine default intervals Use safety factor or statistical methods for failure modes with safety consequences -403, 3.5.6, Appendix B
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Unit III Module 4 - Hard Time Task
Considerations: Task Development Ensure consideration of induced infant mortality failures from rework or overhaul tasks Ensure rework or overhaul tasks returns item to original condition or a reduced interval may be required after overhaul or rework -403, 3.5.6, 5.4,
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Unit III Module 4 - Hard Time Task
Introduction Learning Objectives Task Development Module Objective Provide information for evaluating and developing a Hard Time task. Review and Summary Questions to be addressed Wear Out Survival to Wear Out Age Task Interval Weibull Analysis Testing Fatigue Analysis Default Methods 7 Fly-ins
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End of Module up next…….. Failure Finding Task
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